MANUAL OF 
RADIOLOGICAL 
SAFETY 
NAVMED P-1283 
Rev. March 1948 
Bureau of Medicine and Surgery 
U. S. Navy Department CONTENTS 
CHAPTER Page 
1. The Structure of Matter 1 
2. Structure of the Atom 10 
3. Nuclear Structure 18 
4. Nuclear Transformation 28 
5. Fission of Uranium 50 
6. Slow Neutron Reactions 64 
7. The Atomic Bomb at Hiroshima . 78 
8. Medical Aspects of An Atomic Explosion ... 86 
9. Field Instruments for the Detection of ioniz- 
ing Radiation 101 
10. Medical Aspects of An Atomic Explosion . . . 109 
11. Recovery and Convalescence 120 
12. Treatment 122 
13. Some Thoughts on Disaster Relief 124 
APPENDICES 
1. U.S. Navy Radiological Safety Regulations ... 141 
2. Excerpts from the Interstate Commerce Com- 
mission Regulations for transportation and 
shipping of radioactive materials 166 INTRODUCTION 
It is desirable that all medical officers, in fact all 
medical personnel, have some general knowledge of the 
problems relating to the atomic bomb and atomic warfare. 
In this connection, it is particularly important that they 
understand some of the strategic and tactical applications, 
the limitation of defensive measures, and the problems en- 
countered in radiological safety operations. They should 
have some understanding too, of the devices employed in 
detecting and measuring radiological hazards, the principles 
of avoidance, and also the relationship of medical personnel 
to commanding officers in the capacity of technical advisor. 
It is emphasized that radiological safety implies all. of the 
phases of atomic explosion from the initial production of 
fissionable material until long after the actual bomb burst. 
The medical officer must include within his province not 
only his normal medical duties but also his duties as a 
staff officer, a technical advisor, and a supervisor in 
matters of preventive medicine and decontamination. 
An attempt is made, therefore, to include herein a 
brief, and it is hoped interesting, summary of fundamental 
information which will give all medical personnel a concept 
of the problems involved and a basis for further training 
in this most important field of medicine. The possibilit- 
ies of atomic medicine are as unlimited as those of atomic 
warfare and it is hoped that enough interest will be 
manifested by those who read this to necessitate the pre- 
paration of more advanced courses of personalized instruc- 
tion for those who request them NUCLEONICS 
THE STRUCTURE OF MATTER 
Molecules and Atoms 
The Non-Continuity of Matter 
It will be advantageous to examine our ideas of the 
world about us, forgetting for the moment that we have 
ever heard of atoms and molecules. Let us naively base 
our ideas on only those conclusions which we can draw 
from our five senses. For example, consider the struc- 
ture of a simple block of lead. K we have a six-inch 
cube, we know that we could cut the lead into smaller 
cubes with little difficulty. We might be able to make a 
quantity of smaller cubes one-tenth or even one hundredth 
of an inch in thickness. Is this the limit of division? No- 
with intricate machinery, such as that used in manufactur- 
ing the gratings of spectroscopes, we could make even 
smaller division of lead, down to a ten-thousandth of an 
inch. 
Is there, then, any limit to the subdivision of the 
material which we could accomplish, provided that we 
could obtain suitable machinery? Yes, it has been found 
that this subdivision could not be continued beyond a fig- 
ure of approximately 1Q-8 cm> (10-8 1 . q.000,000,01) 
108 
and still have the material retain its identity and charac- 
teristic properties. The smallest particle which retains 
the properties of the substance in question is known as 
the MOLECULE. 
We need not confine our thoughts to solid materials. 
Imagine the division of a drop of water into smaller and 
smaller droplets until the ultimate molecular size is ex- 
tremely small, there will be a great many of these mole- 
cules in even a small quantity of material. Thus the num- 
ber of molecules in a teaspoon of water is about 23 
(1 followed by twenty-three cyphers). This huge figure is 
more than the number or drops of water in Lake Michi- 
gan. It is also the approximate number of molecules in 
1 the same volume of all common liquids and solids, the 
densities of which do not vary greatly, and the molecular 
structures of which are not too complicated. 
However, we know that gases are much less dense 
than liquids and solids, so that a given volume of any mat- 
erial in the gaseous state will contain fewer molecules 
than an equal volume of the material in the liquid or solid 
state. For example, if we heat the spoonful of water un- 
til it vaporizes into steam at atmospheric pressure, it will 
then occupy a volume of approximately five liters or about 
300 cubic inches. The increase in volume has been over 
a thousand fold, and since the number of molecules pre- 
sent has not changed, we must conclude that most of the 
gas or steam consists of empty space. This must be true 
unless the molecules themselves have expanded, an 
assumption which has been proved false. 
Thus it can been seen that the gas or vapor does not 
consist of continuous matter, but of great empty spaces, 
with molecules of matter scattered in these spaces. Even 
with the denser solids and liquids, it can be shown that a 
large proportion of the volume they occupy is also empty 
space. This will be explained shortly. 
The Kinetic Theory 
There are many common characteristics of gases 
which can be explained from the molecular assumption. 
We know that if we take a certain volume of a gas 
as in a cylinder fitted with a piston, the gas volume will 
decrease if pressure is applied to the piston, and increase 
when the pressure is released. Also, if the gas is heated 
without changing the pressure on it, we know that it will 
expand. When it cools, the volume will decrease. To 
retain the same volume during the cooling process, the 
pressure on the piston must be reduced. 
Observations such as these have led to the develop- 
ment of the kinetic theory of gases. In brief, it is 
assumed that the molecules of a gas act like tinv. hard 
spheres of matter, and that they are in constant motion inside 
their container, flying about at great speed in all direc- 
tions. The space between the molecules is large, so that 
they can go some distance before colliding with one an- 
other or with the walls of the container. When they do 
collide, the collisions are elastic, meaning that no energy 
is lost; the kinetic energy is merely transferred from 
one molecule to another. If the gas is cooled, the mole- 
cules move more slowly - if it is heated, they speed up. 
2 These assumptions explain many of our observations 
on gases. The pressure of the gas is caused by the im- 
pact the many collisions of the molecules against the 
container walls. Thus, if the 
size of the container (and the 
gas volume) is decreased the 
molecules become more crow- 
ed; there are more of them 
striking the wall in a given 
time; consequently the impact 
(pressure) rises. A very sim- 
ple relation exists here, expre- 
sed as = w^ere P 
is pressure, V is volume, and 
the subscripts refer to the con- 
ditions initially and finally. Of 
course, the amount of mass of 
the gas must remain constant, 
and units of P and V must be consistent. Furthermore, 
the temperature must not change during the experiment. 
The temperature effects on the gas can also be ex- 
plained by the kinetic theory. When the gas is heated, the 
molecules move more rapidly, and thus exert a greater 
impact on the container walls. This Increased impact 
raises the gas pressure. However, if it is desired to re- 
tain a constant pressure, the volume of the gas must in- 
crease, so that there will be fewer of these more vigor- 
ous collisions per second on a given area of the container 
than There were before the gas was heated. At constant 
volume, the relation is = PoTand at constant pres- 
sure Vi/T-l = Vg/Tg. Here T is temperature ex- 
pressed in degrees above absolute zero. Absolute zero 
is the temperature at which the molecular motion ceases 
entirely, and is the lowest temperature theoretically ob- 
tainable. It has the value of 273° below zero on the cent- 
igrade scale, and 460° below zero on the Fahrenheit. 
One more useful concept about gases is embodied in 
“Avogadro’s Law,” which states that equal volumes of 
gases at the same pressure and temperature contain equal 
numbers of molecules. This law was based on evidence 
observed in the combination of various gases, and has 
led to many useful conclusions. The reader is requested 
to remember what was just said about the motion of gas 
molecules, and collisions between various molecules. 
The distance which a molecule moves on the aver- 
age before colliding with another molecule, is known as 
Fig. 1 Molecular Motion 
According to Kinetic Theorgy. 
3 the mean free path. This 
will be discussed in more de- 
tail in a later section. The 
mean free path depends on 
the pressure, and the nature 
of the gas itself. Under or- 
dinary conditions of tempera- 
ture and pressure it has a 
value of about iq-5 cm. for 
all common gases. 
It must not be concluded 
that all molecules are simple 
structures - many very com- 
plex. Most molecules are 
not spheres, as we have as- 
sumed above for purposes of 
simplification. Actually they 
vary greatly in size and stru- 
cture, from the very simple 
helium molecule to the com- 
plex ones of glass, proteins, 
or synthetic rubber. The 
molecular weights of these 
complex molecules may be as 
high as a million. The mole- 
cular weight of a substance 
is defined as the weight in grams of a fixed number of its 
molecules. This fixed number is called Avogadro's num- 
ber and is about 6 .0 x 1023. it is not so important to 
know this number, as to remember an important conclusion 
based on the definition of the molecular weight. Since a 
molecular weight of any particular substance contains the 
same number of molecules CAvogadro’s number) as a mole- 
cular weight of any other substance, the ratio of the 
weights or masses of individual molecules is the same as 
the ratio of their molecular weights. 
To demonstrate the magnitude of molecular sizes, 
suppose we try this simple method of measuring mole- 
cular diameter: Let us take a known quantity of an oil 
and allow it to spread into a film on the surface of a tank 
of water. If we confine the film by a wire frame with one 
movable edge, then pull out this movable edge to a certain 
point, we find that the film reaches a maximum size, and 
then breaks, becoming spotty or discontinuous. It is rea- 
sonable to assume that the film has stretched until it is 
only one molecule thick, and has then broken when it 
could stretch no farther. Now measure the area of the 
Fig. 2 Molecular Mean Free 
Path, The dark molecule's 
■oath is traced as it col- 
ides with the container 
walls at ooints A and D( 
and with the other mole- 
cules at B and C, The av- 
erage distance between 
successive collisions at 
B and C is defined as the 
molecular mean free oath. 
4 frame. From the weight of the oil (measured before the 
oil was placed on the water) and from its molecular wei- 
ght determined by an independent experiment, the number 
of molecules in the film may be calculated. We can then 
calculate the area occupied 
by each molecule, and from 
this the molecular diameter. 
Answer - molecular diamet- 
ter = 10-8 cm. approximately. 
We have seen that the mole- 
cule is the smallest division 
of matter which allows a 
particular substance to retain 
its identity and characteristic 
properties. Since there are 
so many different materials 
on earth, there must be many 
different kinds of molecules. 
Thus we have molecules of 
water, sugar, salt, glass, hy- 
drogen, etc. Several hundred 
thousand different substances 
occur natural! ana are Known to the chemist. Not content 
with this quantity, the chemist synthesizes rayon, n$on, 
synthetic rubber, sulfa drugs and dyes, making tailor-made 
molecules of the desired properties, to suit his particular 
needs. Today, he has made over a half million different 
molecules not found in nature, and there is no reason to 
think that he cannot make many more. Hence, if there 
were no simpler method of classifying the various sub- 
stances than by the molecules which compose them, chemis- 
try would be even more complicated than it is, and would 
be as much a puzzle to the average chemist as to the aver- 
age layman. Fortunately, the situation is not so bad. Further 
classification of substances is possible. 
The Atom 
It has been found that these multitudinous chemical 
materials are composed of only ninety-two stable elements 
and several hundred of their isotopes (which will be ex- 
plained later), plus a few more recently discovered un- 
stable elements. We define these elements as materials 
which can not be further subdivided into simpler substanc- 
es by any chemical means. 
The smallest division of an element, we call the atom. 
Thus we have the elements oxygen, carbon, hydrogen, iron, 
lead, etc,, and can talk about atoms of these materials. 
Fig. 3 Determination of 
Molecular Diameter. 
5 But sugar is not an element 
since it is composed of atoms 
of carbon, hydrogen and oxy- 
gen, which are combined into 
sugar molecules. Since the 
sugar molecule can be broken 
down by chemical means into 
smaller and simpler units, we 
cannot have sugar atoms. 
Likewise, salt is a combina- 
tion of atoms of chlorine (Cl) 
and sodium (Na), two more 
elements. 
Chemical Reactions 
The atoms combine with 
one another to form molecules 
under proper conditions, and 
tthere is always an energy 
effect which accompanies their combination. (There are a 
few examples of materials, the molecules of which are 
composed of single atoms, e.g., helium, argon.) Thus a 
pound of hydrogen combines, or burns, with eight pounds 
of oxygen to form nine pounds of water, and in so doing 
liberates energy in the form of approximately 60,000 btu 
of heat. A btu (British thermal unit) is the amount of 
heat necessary to raise the temperature of one pound of 
water by one degree F. This combination of hydrogen and 
oxygen gives enough heat to raise the temperature of 340 
pounds of water from its .freezing point to its boiling point, 
or to convert 44 pounds of ice to steam. Such a reaction 
is called “exothermic,” which means that it liberates heat. 
If we wish to recover the original hydrogen and oxy- 
gen from our nine pounds of water, we would have to add 
to it 60,000 btu of heat, or its equivalent in other energy 
forms, to break the water molecules apart. We might do 
this by heating the water to a sufficiently high temperature, 
or by running an electric current through it. The latter 
would be a more practical method. We conclude that 
since 6Q000 btu (or its electrical equivalent of 16 kw. hrs.) 
is needed to break this quantity of water molecules into 
their component atoms, these atoms must be held to- 
gether with a considerable force. 
There are also many examples of “endothermic” re- 
actions, in which heat must be added to cause the reaction 
to proceed. Thus, if we took a pound of hydrogen and com- 
Fig. 4 Molecules of 
Slnrole Materials. 
6 bined it with twelve pounds of carbon under conditions 
which would result in the formation of acetylene, we would 
find it necessary to add 52,000 btu to make the reaction 
go. Consequently, we should not expect the acetylene 
molecule to be very stable. As a matter of fact, it is 
very unstable, the molecules tending to break down into 
elemental carbon and hydrogen atoms; the liberation of 
considerable energy accompanies this reaction. This is 
the reason why so many precautions must be observed in 
the packing of acetylene cylinders for bottled gas uses. 
Special materials must be added to the acetylene to pre- 
vent its spontaneous decomposition with disastrous results. 
The chemist often says that compounds such as 
acetylene are in a “metastable” state, meaning that they 
can spontaneously break down, with the liberation of 
energy. Water is stable, chemically speaking. There is 
no chance that water at room temperature will break down 
into hydrogen and oxygen, unless a large amount of energy 
is put into it. 
It will be useful to point out an analogy from 
hydraulics to illustrate chemical reactions. Let us con- 
sider spilling a bucket of water on a level floor. There 
is no tendency for the water to move from its position, 
and it can do no work. Nor has it any potential energy. 
It is in a stable condition. Now suppose we spill a bucket 
on a hill side. We know that the water will flow down hill, 
and can do work in “seeking its level,” the amount of 
work depending on the height from which the water flows. 
This water is in an unst±de position. A third example is 
a bucket of water in a crater on top of the hill. 
We know that it is possible to get work from the water 
if it flows down hill, but first we must lift it over the lip 
of the crater so that it can flow down hill. Thus, it is in a 
a metastable condition. The amount of energy which we 
ACTIVATION 
ENERGY 
METASTA-BLB 
UNSTABLE 
STABLE 
Fig. 5 Stable, Unstable and Metastable States. 
7 obtain from the water in flowing down the hill is similar to 
the heat of reaction which was obtained in the combination 
of the hydrogen and oxygen, or the decomposition of the 
acetylene. Similarly, the amount of work we must do to 
raise the water over the lip of the crater is analagous to 
what the chemist calls “activation energy/' and is the 
amount of outside energy -which must be added before the 
reaction will begin. 
We ask the reader to study carefully the concepts of 
reaction and activation energy and of stable, unstable and 
metastable states, as these terms will be used during the 
course of the subsequent discussions. 
To recapitulate, we see that molecules, are formed 
from atoms in various combinations, and that the stability 
of the molecules depends on the energy relations of their 
formation. The chemist writes “equations”, which are 
merely shorthand notations of the reactions involved. For 
example, if hydrogen combines with oxygen to form water, 
we write — 
2 H + 0 = HgO. 
In longhand this means that two atoms of hydrogen 
combine with one atom of oxygen to form one molecule of 
water. Or two million atoms of hydrogen combine with 
one million of oxygen to form one million molecules of 
water. Or again 6.0 x 1023 atoms of oxygen combine with 
12.0 x 1023 of hydrogen to form 6.0 x 1023 molecules of 
water. We recall that the figure of 6.0 x 1023 was the 
number of molecules of any substance which has be de- 
finition a weight equal to the gram molecular weight of 
that substance. The word “mole” or “gram mole” is 
just an abbreviation for either gram molecular weight or 
gram atomic weight. Thus, we say that two moles of 
hydrogen atoms plus one mole of oxygen atoms form one 
mole of water. 
We have said that molecules are formed by the com- 
bination of various atoms. Most molecules are formed 
from atoms of different elements, but some molecules are 
formed from two or more atoms of the same element. Thus, 
two atoms of hydrogen form a molecule of hydrogen, and 
two atoms of oxygen form a molecule of oxygen. However, 
a molecule of helium contains only one atom , while under 
certain conditions a molecules of sulphur consists of eight 
sulphur atoms. Since elements are usually in molecular 
form during chemical reactions, the chemist prefers to 
write his equations in molecular rather than atomic form, 
thus: 
8 2 Hg + Og » 2 HgO 
4 gm + 32 gm = 36 gm 
The weight of a mole (6.0 x 1023) of hydrogen atoms 
is one gram; there are two atoms to a molecule; and we 
used two moles of hydrogen. Therefore, the weight of 
hydrogen is 1 x 2 x 2 = 4 gms. Likewise, the weight of a 
mole of oxygen atoms is 16 grams, there are two atoms 
to the molecule, and we used one mole; hence; there are 
16x2x1 = 32 gm oi oxygen. Each molecule of water con- 
sists of one atom of oxygen and two of hydrogen, and there 
will be 16 plus 2x1= 18 gms per mole of water. Since 
we have two moles of water, the weight of the water is 
2 x 18 = 36 gms. 
Notice that the number of atoms of each element is 
the same on the left side of the equation as it is on the 
right, and the total weights are also the same. This is 
why we speak of the shorthand statement as a “chemical 
equation”. This is not surprising since we have pre- 
viously said that atoms cannot be destroyed by chemical 
means, and common sense tells us that we should not lose 
or gain any mass of weight in the reaction. When we con- 
sider nuclear reactions, a little later on, we will see that 
these statements are not altogether true. 
9 STRUCTURE OF THE 
ATOM 
PROTONS, ELECTRONS AND NEUTRONS 
The Electrical Nature of Matter 
In the first section we saw how all matter is com- 
posed of fundamental building blocks called molecules, 
which are the smallest structural units retaining the id- 
entity of a substance. We also saw that the molecules in 
a gas are far apart, and are moving back and forth in 
empty space like little, hard spheres. It was then stated 
that molecules are composed of atoms, in various arrange- 
ments, and that all of the many thousands of chemical 
compounds can be formed from only ninety-two stable ele- 
ments. The stability of compounds depends upon the en- 
ergy relations of their formation from their component 
atoms. 
We also found that the diameter of the molecule is 
about 10"° cm. This is only an approximate size, as -we 
should expect the heavier and more complex molecules, 
composed of many atoms, to be larger than the lighter, 
simpler ones. However, if one recalls from his geometry 
that the volume of a sphere is proportional to the cube or 
its radius, he will see that there can be considerable var- 
iation in molecular volume and weight, without the 
molecular diameter changing very much. This is assum- 
ing the molecules to be spherical. 
What about the size of the atom? It is believed that 
the atoms in a molecule are very close together, even 
overlapping one another (we shall see shortly how this is 
possible), so that atomic diameters are of the same order 
of magnitude as molecular diameters. For simplicity we 
shall assume that the atomic diameter is also about 10"° 
cm. 
The question now arises concerning the structure of 
the atom. Is the atom merely a little hard sphere? If so. 
10 what is the reason for atoms 
to unite into molecules? What 
is the nature of the forces 
binding the atoms? 
Let us see what we can 
do about answering some of 
these questions. Although 
most of the knowledge con- 
cerning the structure of the 
atom has been revealed dur- 
ing the past fifty years, even 
as far back as the middle of 
the 19th century the problem 
was undergoing extensive in- 
vestigation. The famous Eng- 
lish scientist, Michael Fara- 
day, discovered some very 
interesting information by 
running d.c. electrical current 
through water mixed with a 
little acid. (See figure 6). For example, he found that the 
current broke water into its fundamental elements, and 
that gydrogen collected at the negative electrode (cathode) 
while oxygen collected at the positive electrode (anode). 
The volume of the hydrogen was exactly twice that of the 
oxygen. This is just what we would expect, since one 
molecule of oxygen always combines with two molecules 
of hydrogen, and by Avagadro’s Law, we know that equal 
volumes of gases under the same conditions of pressure 
and temperature contain equal numbers of molecules. 
Faraday also found that for the same amount of 
electricity run through the solution, the same number of 
molecules of hydrogen would always be formed. The for- 
mation of one mole of hydrogen atoms, or a half mole of 
hydrogen molecules, requires a unit of electricity known 
as the faraday, which is 96,500 coulombs. A coulomb is 
simply the number of negative electric charges carried 
by a current of one ampere in one second. By studying 
the “electrolysis” of many materials, Faraday found that 
in order to deposit a mole of an element, one, two, three, 
up to eight faradays were required, depending on the 
element in question.. Thus, one faraday was required to 
deposit a mole of hydrogen, sodium, chlorine, or silver, 
while copper, magnesium, and oxygen two, and 
aluminum three. How can we explain Faraday's results? 
By passing a current through some molten sodium 
chloride (NaCD which is the chemical name for common 
Fig. 6 Faraday's 
ment Electrolysis of 
Water. 
11 table salt, we can conduct, an experiment which is a little 
easier to understand than Faraday’s, but still based on 
the same principle. In this experiment, the salt is bro- 
ken down into its elements, chlorine collecting at the 
anode, and sodium at the cathode. (See figure 7.) 
Since like charges repel and unlike charges attract, we 
conclude that sodium atoms carry a positive charge and 
chlorine a negative charge, and that the charges on these 
atoms are neutralized by opposite charges at the elec- 
trodes. 
The chemist says that sodium and chlorine atoms in 
the molten state are really not normal atoms, but have 
charges - the sodium a positive charge and the chlor- 
ine a negative charge. Such charged atoms are called 
ions, and the process of producing them is known as ion- 
ization. Since unlike charged bodies attract, the sodium 
and chlorine ions are attracted toward each other and 
combine to form sodium chloride molecules. This at- 
traction is sufficiently strong to form the stable molecule 
in the solid state. However, if the salt is melted, the 
molecules are broken down into ions, and these ions con- 
duct an electric current. The ions are then neutralized 
at the electrodes and the un-ionized atoms collect as the 
free elements. 
By extending this explanation to other materials, we 
can deduce that oxygen and copper ions must carry twice 
as much charge as chlorine and sodium ions, since two 
faradays are required to produce a mole of copper or 
oxygen. Similarly, since aluminum requires three fara- 
days per mole, it must be triply charged. 
Such observations as those we have described, coup- 
led with others in the fields of radioactivity, spectros- 
copy, etc., which we do not have time to discuss, led 
scientists to conclude that the forces holding atoms to- 
gether are largely electrical in nature. The atoms 
themselves consist of bundles of electrically charged part- 
icles, both positive and negative. The positive and nega- 
tive quantities of electricity are equal, so that the atom 
as a whole is electrically neutral. However, this does 
not mean that the various parts of the atom are neutral. 
Ionization is explained as the process of losing or gain- 
ing electrical charges by the atom. Thus, if an atom loses 
a negative charge, it becomes a positive ion, while if it 
loses a positive charge (or gains a negative charge, which 
would have the same effect), it becomes a negative ion. 
12 Bohr's Model of the Atom 
As we just saw, the atom 
is really an aggregation of 
charged particles of matter, 
half charged positively and 
half charged negatively. Ear- 
ly workers, such as J.J. 
Thomson, thought that the 
atom was like a bean bag 
filled with equal numbers of 
“positive” and “negative” 
beans homogeneously distri- 
buted in the bag. (See figure 
8.) But experiments carried 
on by Lord Rutherford and 
others showed that this could 
not be a true representation 
of the atomic model. Let us 
consider what would happen 
if we started to shoot at one 
of the bean bags with a high 
speed B-B-gun, or a low speed 
22 rifle. We would expect the 
bullets to be slowed down in going through the bag, and 
slightly deflected from their course by collisions with the 
beans in the bag. In fact, if we knew the size and den- 
sity of the beanbag and the mass and velocity of the 
bullet, it would not be too difficult to calculate just how 
much the bullets would be deflected and slowed. Ruther- 
ford carried on such experiments, except that he shot at 
atoms instead of bean bags, and for bullets he used high 
speed particles, called ‘alpha particles”. There will be 
discussion of the origin and nature of these alpha particles 
in 
Rutherford had enough information to calculate how 
much his alpha particles should be deflected, but the re- 
sults did not agree at all with his calcula- 
tions. He found that most of his bullets 
were deflected only a very small amount, 
while a very few were deflected greatly, 
some even being reflected backwards by the 
atom. His calculations indicated that all of 
them should be deflected at some intermed- 
iate value. The only way that Rutherford 
could explain his results way by assuming 
that instead of being composed of a homo- 
Fig* 7 Electrolysis of 
Salt. 
Fig 8 Thom- 
son* s Model 
of the Atom 
780893 0—48 2 
13 geneous mass of material, the atom was really composed 
of a very dense, small center, or nucleus, plus a shell of 
lighter particles at a considerable distance from the nucl- 
eus. Rutherford reasoned that most of the volume of the 
atom is merely empty space. 
Several years later Niels Bohr, a Danish Physicist, 
assembled all of the available data of physics and chem- 
istry on atomic structure, and presented his theory of the 
atom. This theory has explained a great many of the 
phenomena observed, and is of such value that Bohr was 
awarded the 1912 Nobel prize. Prof. Bohr has also con- 
tributed important work to the atomic bomb project. 
According to him the atom really looks a great deal like 
our solar system. At the center is a massive, dense 
nucleus, corresponding to our sun. At a great distance 
away from the center are many lighter particles, which 
spin around it in circular or elliptical orbits, just as the 
earth and other planets revolve around the sun. Just as 
most of the volume of the solar system is empty space, 
similarly, the atom, a miniature solar system, also is 
mostly empty space. Bohr said that the central mass was 
composed of a varying number of closely packed, positively 
charged, heavy particles, called protons. The particles 
flying around the nucleus are much lighter, and are neg- 
atively charged. These are called electrons. 
According the Bohr, the properties of elements are 
completely determined by the number of protons and elec- 
trons contained in the atoms of the elements. We present 
diagrams of a few 01 the simpler atoms, asking the read- 
er to pay particular attention to the small volume occup- 
ied by the nucleus, and the large amount of free space. 
(See figure 9.) We also emphasize the small mass of the 
electron as compared to that of the proton. The proton 
is about 1840 times heavier than the electron, so that the 
mass of the atom is mostly determined by the number of 
protons. Thus, an atom of hydrogen, which has only one 
protom is said to have a mass of one. The next atom, 
that of helium (He) has a mass of four (relative to hydro- 
gen), although it has only two protons. The rest of its 
mass comes from the presence of two additional funda- 
mental particles, called neutrons. 
It is not believed that the neutron actually is a pro- 
ton plus an electron, though the mass considerations are 
approximately correct. A positron and a neutron do not 
even theoretically give a proton, since the neutron already 
weighs more than the proton before anything is added. A 
posilron is merely a particle equal to an electron in mass 
and carrying an opposite charge. Thus the neutron has no 
14 charge, but its mass is nearly the same as that of the pro- 
ton, since the electron contributes only a very small am- 
ount of mass. Sometimes, we speak of protons and neu- 
trons under the common name of nucleons, since they are 
both found in the nucleus. Except for the difference in 
charge, and properties related to charge, there is no 
great difference in the properties of the two particles. 
Theoretically at least, we see that a proton can become 
a neutron if its charge is neutralized by that of a nega- 
tive electron. Conversely, the neutron can be converted 
to a proton by combining with a particle known as a posi- 
tron. This is a particle which has the same charge and 
mass as an electron, but its charge is positive rather 
than negative. Positrons are not very common, and we 
will not be concerned with them for the present. We must 
emphasize that the combinations of the various particles 
as just given, are presented only as an aid in forming 
a picture of the relationship between them. This present- 
ation does not give a strict explanation of the actual pro- 
cesses occurring, as these processes are much more 
complicated. 
Reconsidering, we now say that the mass of an atom 
is determined by the' sum total of its protons and neutrons. 
However, the chemical properties of the element or atom 
are determined by the electrons which it contains. The elec- 
trons are in various orbits around the nucleus, and we can 
easily see that the total number of external electrons must 
be the same as the numberof protons in the nucleus, since the 
atom as whole is electrically neutral. The atoms of each 
element possess a definite number of orbits in which the 
electrons revolve, and these orbits are at fixed distances 
from the nucleus. Some of the orbits are called stable or 
“unexcited,” since the atoms are in their most stable sta- 
tes when the electrons are revolving in these orbits. The 
other orbits are “excited” and correspond to less stable 
states. Energy is emitted when an electron moves from 
an excited to a stable orbit. The energy is manifested by 
electromagnetic radiations, such as ultra-violet, visible, or 
infra red light, and gives rise to spectral lines. Each 
element has its own characteristic spectral lines, and 
studies of them give much information on atomic structure. 
For hydrogen there is only one unexcited orbit; for 
lithium there are two, and so on. The orbital arrangement 
becomes very complex for heavy elements, which contain 
jnany protons in their nuclei and therefore many electrons 
outside the nucleus. 
Of particular interest to the chemist are the electrons 
in the outermost orbit, the so-called “orbital electrons.” 
These determine the valence of the element- The valence 
15 HYDKOG-EN 
HELIUM 
LITHIUM 
OXY& EN 
Fig. 9 Rutherford-Bohr Atomic Models. 
of an element is merely the number of hydrogen atoms 
one of its atoms will combine with, or if the element does 
not combine with hydrogen, it is the number of hydrogen 
atoms one of its atoms is equivalent to, or will replace. 
Thus, since the formula for water is EhjO, one oxygen atom 
combining with two hydrogen atoms, the valence of oxygen 
is two. If we combine copper (Cu) with oxygen, we get a 
compound CuO or copper oxide. Here the copper has re- 
placed the two hydrogen atoms, and its valence is also 
two. Similarly for aluminum the valence is three, and so 
on. 
Another way to determine the valence of an element 
is by electrolysis of one of its compounds. The number 
of faradays required to obtain a mole of the atoms of the 
element in question is also its valence. This method per- 
mits distinction between the elements with oositive valences 
1G and those which have negative valences. If the element 
combines with hydrogen, or is deposited at the anode on 
electrolysis, its valence is nagative. If it replaces hydro- 
gen, or is collected at the cathode on electrolysis, its 
valence is positive. 
The number of protons in the nucleus (or of electrons 
outside the nucleus) is very important, in determining chem- 
ical properties, and is spoken of quite frequently as the 
atomic number Z. The atomic weight, A, is also impor- 
tant, especially in determining the physical properties of 
an element. The atomic weight is equal to the total num- 
ber of protons and neutrons, as stated previously. We will 
make frequent use of these two numbers. The values of 
A and'Z for the various elements may be found in the 
Periodic Table, which is a systematic arrangement of the 
elements according to their atomic numbers, (See page 
49.) This is a handy reference chart. 
17 NUCLEAR STRUCTURE 
FISSION AND FUSION 
Isotopes 
We have said that an element is completely defined 
in structure and in properties by its atomic number and 
atomic weight. Of the two, the atomic number is the more 
important, since it determines the chemical properties, 
energies of reaction, etc. it is possible for two atoms to 
have the same atomic number, but different atomic weights 
Such atoms, differing only in the number of neutrons In 
their nuclei, are known as Isotopes. 
Practically, every element as found in nature is 
really a mixture of two or more isotopes. Thus, ordin- 
ary hydrogen consists of three isotopic forms, all of 
which have an atomic number of one, but possess atomic 
weights of 1, 2, and 3. The isotope of atomic weight 1 is 
by far abundant, composing about 99.98% of the 
total hydrogen. The isotope of atomic weight 2 Is 
known as deuterium or “heavy hydrogen,” and occurs to 
the extent of only 0.02% of the total hydrogen. The third 
Isotope, called tritium, is even less abundant than deu- 
terium, and not of much interest to us. (See figure 10.)- 
Since deuterium has an atomic number of one, and an 
atomic weight of two, it must consist of a nucleus contain- 
ing one proton and one neutron, and have one electron 
revolving around the nucleus. If we remove the electron 
from the deuterium atom, we have produced an ion, called 
deuteron. Obviously this ion has twice the mass of a 
proton, but the same charge as the proton. Deuterons are 
important “bullets” for use in bombarding the atom in 
experiments similar to that of Rutherford, described on 
page 13. 
We find that the Isotopic forms of hydrogen exist not 
only in the free state, but also in compounds. The same 
is true of the Isotopes of the other elements. As an ex- 
ample, when hydrogen combines with oxygen to form water, 
it forms not only HgO of molecular weight 18 (16 plus 2 x 
I), but also a small quantity of D2O of molecular weight 
20 (16 plus 2x2). The latter is known as “heavy water” 
18 and is important in nuclear 
physics work. The proportion 
of heavy water in ordinary 
water is, of course, on 0.02%, 
but there are means of sepa- 
rating the two. 
With most substances, the 
ratio of one isotope to all 
the others is so high that the atomic weight of the mix- 
ture is practically that of the most abundant one, and the 
atomic weights, in ratio to that of hydrogen, are whole 
numbers. This would be expected, since most of the 
weight of the atom is in its nucleus, which is composed of 
an integral number of protons and neutrons of very nearly 
the same weight. In fact, the observation that most atomic 
weights are integral multiples of that of hydrogen was one 
of the first pieces of evidence for the existence of the 
nuclear particles, and a strong basis for the atomic theory. 
However, the isotopes may be present in nearly equal 
proportions, in which case the atomic weight will not be 
near a whole number. This is true for chlorine, which 
has an atomic weight of 35.5. For a long time chemists 
were at a loss to explain this discrepancy. Later it was 
clarified by the discovery that ordinary chlorine is a mix- 
ture of isotopes of atomic weight 35 and 37, in the ratio 
three to one. The value of 35.5 is merely the weighted 
mean of these two numbers. 
The device by which isotopes were discovered and 
measured is known as the mass spectrograph (See figure 
11). 
The principle of its operation 
is that ionic isotopes of dif- 
ferent masses will be deflect- 
ed by different amounts when 
placed in a magnetic field. 
The atoms to be studied are 
ionized by means of an elec- 
trical discharge and confined 
in a narrow beam by being 
made to pass through a series 
of narrow slits. They are then 
led into a strong magnetic 
field, which deflects them from 
their straight line path into 
paths which are circular arcs. 
Those readers, who are 
familiar with the “right 
Flg« 10 Isotopes of Hydrogen. 
Pig* 11 Simplified Mass 
Spectograph, 
IS hand rule for motors" in electricity will recall that a 
wire carrying a current in a magnetic field perpendicular 
to it, will be deflected in a direction at right angles to 
both the wire and the field direction. The force causing 
the deflection is proportional to the current strength. 
Since a stream of ions is really an electric current, the 
same situation will hold for such an ionic stream. Here 
the deflecting force is proportional to the ionic velocity. 
Accelerating the ions in an electric field before they 
enter the magnetic field gives a uniform energy to all of 
them. The velocity of the heavy ions is then less than 
that of the light ones; consequently the heavy ones are 
less affected by the magnetic field. The heavy ions move 
in a circle of large radius and carf be collected through 
a slit, or caught on a photographic plate. The light ions, 
being more affected by the magnetic field, move in a 
of smaller radius (greater curvature), and can be 
collected in a slit a distance away from that of the heavy 
Ions, or caught on a plate at another position. From the 
positions at which the ionic beams struck the photographic 
plate, Aston, the Inventor of the mass spectrograph, was 
able to measure isotopic masses with great accuracy. We 
shall see in the next section the Importance of obtaining 
very precise isotopic masses. 
Inside the Nucleus 
The observant reader will notice that there has been 
a purpose in our presentation during the first three sec- 
tions. Beginning with an extremely large number of sub- 
stances, in various forms and combinations, we have 
shown that all of these substances are made up of a half 
million or so different molecules. A simplification re- 
sulted when we foungl that all of the molecules would be 
constructed from only 92 or so different atoms or chem- 
ical elements. Then we learned that these atoms are 
really built from only a few very fundamental particles 
—neutrons, protons, electrons, and positrons. 
An even further “simplification’* is possible, says 
the modern physicist who understands quantum mechanics. 
Quantum mechanics finds it necessary to accent hypotheses 
not compatible with the concepts of classical physics.- 
According to quantum mechanics, there are really no 
such things as the different particles; they all are merely 
waves or pulses of energy which can be represented by 
mathematical equations. To the “quantum mechanic/' it 
is immaterial whether or not we can draw a picture or 
conceive of a model consistent with our common concep- 
tions of space and material. Thus the average reader or 
student, unless he has extensive training in advanced 
physics, finds it difficult to visualize what the quantum 
2C mechanic is talking about. In this discussion, therefore, 
we are limited to retaining our antiquated ideas of elec- 
trons and protons, etc., in the interest of simplicity of 
presentation. 
We previously stated that the nucleus of the atom 
is made up of a varying number of protons and neutrons. 
It is convenient to think of these nucleons as little drop- 
lets of a liquid, and the nucleus itself, as a larger drop 
composed of the smaller ones fused together. Of course 
the properties of this nuclear liquid will be considerably 
different from those of an ordinary liquid; for instance, 
its density will be much higher. If we comoart: its den- 
sity to that of an ordinary atom, we find that it is much 
higher than that of the atom as a whole. This follows 
since the atom is composed of mostly empty space, and 
practically all of its mass is concentrated in the nucleus, 
the volume of which is very much smaller than that of 
the atom. The reader can easily calculate for himself 
the-value of the nuclear density, knowing the weight of an 
atom or nucleus, .and its volume, that of a sphere of dia- 
meter roughly cm. The weight of an atom is the 
gram atomic weight of the element considered, divided by 
Avogadro’s number. 
By this method, the nuclear density is shown to be 
tremendous — grams per cubic centimeter, compared 
to one gram per cc. for water. This means that a drop 
of nuclear fluid big enough to be seen would weigh ten 
million tons I Lest the reader doubt the existence of such 
heavy materials, it is interesting to point out that the 
white dwarf star known as the companion of Sirius has a 
density about one hundred thousand times that of water, 
and higher densities than this are believed to have occur- 
ed in the sun and stars before the formation of the pre- 
sent universe. 
One very characteristic and important property of 
liquids is their “surface tension/’ Surface tension is a 
force which tends to make large droplets out of small 
ones. Large droplets have a smaller surface area for a 
given amount of volume or mass than do small ones (See 
figure 12). The surface of a liquid represents potential 
energy, and all systems tend to change into the most 
stable states. Thus, the large droplets dess energy) are 
more stable than small droplets (more energy). The 
reader may check this for himself by remembering that 
the surface of a sphere is 4-tt r2 while the volume 
4 tt r1^ 
is —^— . Thus a drop of radius one cm has a surface 
of 4'Tr'cm2, and a volume of cc, and its surface to 
21 For Bach Sphere 
/SURFACE* 47TF2=4TT CHI2 
volume= 4 nr3- 4 ttcm? 
3 3 
8 DROPS 
f.TOTAL SURFACE* 8X4J=327T CUE 
\ TOTAL VOLUME* 8X4-TT=32 W CtTL? 
SURFACE= 4TT(2)l=IS TTCHlz 
Vol ume=4tt(z)3=32tt cm.3 
3 3 
SURFACE 22 ip 32_ Tf = 3 
VOLUME " ‘ 3 " J 
SURFACE /z-_ . 327T_ J 
VOLUME ‘ 3 ~Z 
Fig. 12 Fusion of Small droplets causes decrease of total 
Surface Area. 
volume ratio Is 3. But a drop of radius two cm has a 
surface of x 22 or 16 n7" cm2 and a volume of 
4 3 32 ‘7F 
x 2 or cc. Its ratio of surface to vol- 
ume is only 3/2. To put it another way, we can use 
these figures to show that the volume of eight drops of 
radius one cm. is the same as that of one drop of rad- 
ius two cm., but the surface area of the eight droos is 
twice as great as that of one drop. If we combine the 
eight small drops Into one large one, there will be a re- 
duction in-the total surface area, and therefore in the 
potential energy equivalent of the surface area of the 
system. Thus when small drops coalesce, to larger ones, 
energy is liberated. This is the reason that small drop- 
lets of mercury on a desk rapidly combine with one an- 
other, when they are brought into contact. The value of 
this surface tension energy is about 75 ergs per square 
cm. of surface (for water). Converting to English units, 
the amount of surface energy is about 10“2 ft. lbs. per 
square foot of surface. This a rather small amount of 
energy. However, the situation is greatly different with 
the nuclear fluid. Here the surface tension is 1019 ergs 
per sq. cm., so that the energy of a square foot of nu- 
clear surface is about 1015, or a million billion ft. lbs. 
per sq. ft., which is quite a lot of energy. 
Evidently the surface tension forces in the nuclear 
fluid are very large, and we would expect the nuclear 
fluid droplets to keep on combining ad infinitum, in order 
22 to liberate more energy. Thus, very large 
and heavy nuclei would be built up. Actually, 
no stable nuclei have yet been observed con- 
taining more than 238 of these nuclear drop- 
lets, or "nucleons. The answer is simply that 
there is another important force which pre- 
vents the nucleons' combining indefinitely 
(see figure 13). 
This is the force of electrical repulsion 
between like charges, often called the “coul- 
omb force" after the man who first set up the 
mathematical laws governing it. Coulomb's 
law is very simple. It states that the repul- 
sion between two like charges is equal to the 
product of the charges divided by the square of the dis- 
tance between their centers. If the charges are unlike, 
the force is attractive. Thus: 
F*e/el 
~Y~ OYNBS 
F — 1 DYNE 
Fig. 13 Culombs 
Law 
Qt e<2 
F = 
r 
where F = force in dynes e 1 , e are the electrostatic 
charges of the first and second bodies in the proper 
units, and r is the distance in centimeters separating 
them. Coulomb's law tells us that when we try to bring 
two protons together to form a bigger nucleus, there will 
be a repulsion tending to keep these protons apart, since 
they are both positively charged and like charges repel. 
However, surface tension forces favor combination, so 
that it is possible to cause the two protons to combine. 
Let us suppose we have successfully combined the 
two protons. Now, if we try to combine two of these 
double proton nuclei to form one nucleus of four protons, 
we will have a repulsive force four (2x2) times as 
great as we had when we tried to combine the single pro- 
tons (1 x 1 ). Hence we see that the coulomb forces in- 
crease very rapidly as we try to make larger and larger 
particles. On the other hand, the surface tension attrac- 
tive forces for combing small nuclei into large ones do 
not increase very rapidly. We saw in the previous exam- 
ple that we had to combine eight drops together to reduce 
the surface hy a factor of only two. Therefore, the cou- 
lomb repulsive forces soon overtake the surface tension 
attractive forces, and make further fusion of nuclei impos- 
sible. When the two forces are exactly balanced, the nu- 
cleus will be extremely stable, since there is no tendency 
for it to break down into smaller parts because of coul- 
omb repulsion ( see figure 14 ), or to fuse together into 
larger ones because of surface tension attraction . 
23 Obviously, this balance 
should occur for a nucleus of 
some intermediate size and it 
turns out to be near silver 
(Ag ), at.wt. 108, at. no. 47, 
which is practically in the 
middle of the periodic table of 
elemtns. Theoretically, all elements which are lighter 
than silver should stabiJ4 ze themselves by forming silver 
through fusion of their nuclei. Conversely, all elements 
heavier than silver should stabilize themselves by breaking 
into smaller parts, or as we say, by “fission”, to form 
the lighter elehaent silver. Further more, the farther a 
heavy elements is situation from silver in the periodic 
table, the more unstable it is, and the more energy can be 
liberated by its fission. Figure 15 shows, the amounts of 
fission and fusion energy, which are direct neasure of insta- 
bility for the various elements. The nuclear physicist uses a 
unil known as the electron volt, the conversion of which in- 
to other energy units may be found in the “English-Metric 
Conversion Table” not included in this publication. Notice 
that the amount of fission instability energy for uranium (U) is 
the highest of any natural occurring element on the chart. 
One is tempted to ask what effect the neutrons in the 
nucleus have on its stability? We have confined our dis- 
cussion to protons alone. Since the neutron has no elec- 
trical charge, we might think that it would be possible to 
bring a great number of neutrons into the nucleus, and 
increase the nuclear stability because of the surface-ten- 
sion forces. This supposition is true to a certain extent. 
With the exception of the very lightest element - hydrogen 
— all stable nuclei contain at least as many neutrons as 
protons. A good way to think of the neutrons in the nu- 
cleus is as buffers, which keep the protons apart, so that 
they cannot get close enough together to upset the nuclear 
equilibrium and blow the nucleus apart. As we put more 
protons into the nucleus, their mutual repulsion increases 
rapidly, so that more neutrons in proportion, as well as 
in total number;, are required. Thus for helium, carbon, 
oxygen, and nitrogen, the ratio of neutrons to protons is 
1/1. For heavier elements the ratio increases. At the 
middle of the periodic table, it is about 1.3/1 for silver, 
and at the end of the table it is up to 1.6/1 for uranium. 
These n/p ratios can be shown'to be the most stable 
arrangments for nuclei according to the quantum theory, and, 
in fact, we shall find later on that a nucleus with too 
many neutrons is just as unstable as one with too few. 
Fig. 1A Electrostatic Repulsion 
causes Fission of Heavy Nuclei. 
24 Fig* 15 Fission and Fusion Instability Energies of.the Var- 
ious Elements* 
FUStON 
/HSTAB/UTy 
F/SS/OM 
msTAStury 
Fig. 16 Fission and Fusion Activation Energies of the Various 
Elements• 
* Term "Mev" used in these figures not otherwise explained. 
A Mev is equal to 1 million electron volts* 
25 Fig, 17 Activation and Fission Instability Energies of Several 
Unstable Nuclei, 
Activation Energy for Fusion and Fission 
From our discussion about nuclear stability, fission, 
and fusion, the question immediately arises, “how can any 
of the elements except silver exist at all — why don't 
they all blow apart or fuse to form silver?” The answer 
lies in the concept of activational energy, which we dis- 
cussed in the first chapter. Before we can get any nuclei 
to disintegrate, we must first supply a quantitiy of activa- 
tional energy. Obviously, the easiest nucleus to attack is 
the one which requires the least activational energy, just 
as it is easier to detonate nitrogelycerin, which goes off 
from merely jarring a battle of it, than it is to detonate 
TNT, which is stable even when a rifle bullet is shot 
thr ought it. 
Figure 16 shows the activational energy for fission 
or fusion of the various nuclei. Note how low the value 
is for uranium. From this low activation energy, coupled 
with its high fission instability energy shown in firgure 
15, one quickly sees that the fission of uranium presents 
an interesting possibility for obtaining large amounts of 
energy. Just how to release this energy by supplying the 
activational energy required is a question we will discuss 
in subsequent chapters. This curve, taken from the data 
of Bohr and Wheeler ( Physical Review, Sept. 1939 ) re- 
♦Terra MMev" used in these figures not otherwise explained, A 
Mev is equal to 1 million electron volts# 
26 presents the fission instability energy as the height of the 
peaks. The craters* depths are a measure of the activa- 
tion energy required for fission. It is well to emphasize 
the difference in scale in figure 17 for the TNT explosion, 
a chemical reaction and the nuclear reaction. Roughly 
20,000,000 times as much energy is liberated per atom of 
U235 undergoing fission as is liberated by a molecule of 
TNT in chemical reaction. 
That differnce seen even in proportion — the actual 
difference in figures being too great for us to really 
grasp — is the difference between previous man-made 
explosions and the atomic bomb. A whole new scale of 
power is involved, with completely different concept. 
27 NUCLEAR TRANSFORMA- 
TIONS 
Radium and Radioactive disintegration 
Most of us have heard of the work of Pierre and 
Mme. Curie in the discovery and identification of radium. 
This work was one of the more important advances of 
modern physics and chemistry. Their findings were pro- 
ceded' by those of Becquerel during the 1890*3 who found 
that a photographic plate, when placed in proximity to ores 
or compounds of uranium, was affected in the same 
manner as if it had been exposed to light. This occured, 
even when the plate was protected by sufficient paper cov- 
ering to assure that even the strongest light could not 
effect it. Becquerel reasoned that there was something 
associated with uranium which produced very penetrating 
rays, which, although not in the visible light range, be- 
haved similarly to light and could blacken a photographic 
plate. That these rays were not appreciably retarded by 
the usual coverings of the plate was evidence of their 
great penetrating power. 
The Curies carried on Becquerel’s work, and showed 
that the active material causing these rays was not uran- 
ium itself, but a hitherto undiscovered element, which 
occurred in very minute quantities along with the uranium. 
They called this new element radium. The reason that 
radium is always found with uranium in natural ores is 
that uranium is an unstable substance, which slowly de-. 
composes to radium. Actually, the picture is very com- 
plicated, since uranium decomposes to a number of other 
unstable elements before radium is formed. And the 
radium also decomooses through a number of intermed- 
iate elements, until it finally forms the stable element, 
lead. Such a sequence of unstable elements is known as 
a radioactive series or “family.” 
There are three such families, deriving from uran- 
ium, thorium, and actinium. U235, the less abundant iso- 
tope of uranium, is really not in the uranium family at 
all, but in the actinium. However, it occurs with uran- 
ium ( U238 ) in nature, because the chemical properties of 
23 the two isotopes are very similar. All three of the rad- 
ioactive families decompose through intermediate steps to 
form lead, although each forms a different isotope of lead. 
. Natural lead is a mixture of these three isotopes plus a 
fourth, Pb204. 
Now, focusing our attention on radium alone, we find 
that radium is decomposing at a measurable and fixed rate 
into another element, a heavy, chemically inactive gas 
known as radon. At the same time the radium is giving 
out certain emanations which are divisible into three dis- 
tinct classes. The first, called alpha rays or alpha par- 
ticles, consists of a number of 
fast moving helium ions. Re- 
calling our picture of the he- 
lium atom - two protons, two 
neutrons, and two electrons - 
we see that an ion can be form- 
ed by stripping off one or both 
of the electrons. Actually, 
both electrons are missing, 
and the alpha particle is simple a helium nucleus. Alpha 
particles are readily detected by means of a simple in- 
strument known as the spinthariscope. (See figure 18) 
The spinthariscope consists of a screen coated with 
a material such as zinc sulphide, and an eyepiece to mag- 
nify the screen." When an alpha particle strikes the 
screen, it causes a transformation of the zinc sulphide, 
which emits a little flash of light. This flash of light is 
magnified by the eyepiece. The same phenomenon occurs 
in the “radium dials’’ of clocks and watches. Here a 
small amount of radium or one of its compounds is mixed 
with some zinc sulphide pigment, so that alpha particles 
are always colliding with the molecules of ZnS, and emit- 
ting light. This emitted light can be observed when the 
dial is in the dark. 
The alpha particles are moving with considerable 
velocities - between 2,000 and 20,000 miles per second, 
or roughly from one to ten percent the velocity of light. 
Because of their high velocities, they have high kinetic 
energies. They are able to penetrate several cm. of air, 
or thin foils of metal (less than a mm. ) before losing 
their energy. They lose a little energy each time they 
collide with another atom, until they are finally stopped. 
The energy of the collisions is dissipated, not as heat, but 
in knocking out the electrons from the atoms with which 
the alpha particle collides. By such collisions ions are 
formed. Thus the alpha particle leaves a number of ion- 
Fig* 18 Spinthariscope 
780898 O—48 3 
29 ized atoms in its wake, and if we are able to observe 
tnese ions, we will at least be able to tell where the alpha 
particle has been. Details of these observations will be 
given in the next section. 
The second type of emanation from radium is known 
as beta rays or particles. The beta rays are nothing more 
than streams of fast moving electrons, which have been 
thrown out of the radium. They travel several hundred 
times farther than the alpha particles, either in air or metal, 
before coming to a stand-still. This is logical, since the 
mass of the alpha particle - two protons plus two neutrons— 
is approximately 7500 times greater than that of ’the beta 
particle. Thus a beta particle, with the same energy as 
an alpha particle, will move much faster than the alpha 
particle, and go farther before its velocity is brought to 
zero by collisions with the atoms which it ionizes. Evi- 
dently then, it will not ionize • as many atoms for a given 
length along its path as will the alpha particle, if their 
energies, and hence the number of ions which they can 
form, are equal. Although the energies of the- alpha and 
beta particles are not exactly equal, they are of the same 
order of magnitude, so that our conclusions are valid. • 
The third type of emanation from radium, known as 
gamma rays, does not consist of particles at all. It be- 
haves very much like light, or better, like X-rays of very 
high frequency. Gamma rays move at the speed of light 
and with wave motion. They differ from light only in 
having a much higher frequency; or putting it another way, 
their wave length is much shorter. In fact, this is the 
main distinction between different types of electromagnetic 
radiations, 'including radio waves, radar, radiant heat, in- 
fra-red, visible light, ultra-violet, X-rays, gamma rays, 
and cosmic rays. The sequence given is in order of in- 
creasing frequency and penetrating power. In order to 
stop gamma rays from radium, several inches of lead are 
required, while several feet of lead or concrete are nec- 
essary to stop those encountered in atomic bomb work. 
Obviously, gamma rays are very penetrating, much more 
so than alpha and beta rays which can be stopped by much 
thinner sheets of metal. 
At this point let us consider the methods of detection 
and counting of these particles from radioactive disinteg- 
ration. One of the simplest is by using the gold leaf 
electroscope, familiar to any student of elementary physics 
( see figure 19 ). When the electroscope is charged, there 
will be an excess of either positive or negative charges on 
the small sphere. These charges will distribute themselves 
over the sphere, the conducting rod and the two thin gold 
leaves which are attached to the rod. Let us suppose that 
30 the sphere is charged posi- 
tively; the gold leaves also be- 
come positively charged. Be- 
cause like charges repel one 
another, the two leaves will 
tend to move apart. This they 
can do easily, since they are 
very thin and light, and only a 
small force is needed to over- 
come their inertia. 
If ions are produced in the 
neighborhood of the small 
sphere, negative ions will be 
attracted to the positive sphere 
and will neutralize its charge. 
The charge on the gold leaves 
Is also lost, and the leaves then 
move back together. The rate with which the leaves move 
back together is proportional to the rate at which the 
charges on the sphere are being neutralized. This in turn 
is proportional to the rate of ion production in the neigh- 
borhood of the sphere; Here the production of ions depends 
on the entrance of charged particles such as alpha or beta 
rays into the surrounding space. Gamma rays are also 
able to produce ions in matter through which they are 
traveling. Thus, the rate of motion of the gold leaves is 
directly related to the rate of entrance of alpha, beta, or 
gamma rays into the space surrounding the small sphere. 
By suitable refinements, it is possible to make very sensi- 
tive and accurate detecting and counting instruments based 
on the simple electroscope. 
The Geiger Counter (figure 20 ) is another useful 
device for the detection and counting of particles from ra- 
dioactive disintegration. The counter consists of two 
electrodes, one a metal cylinder and the other a fine 
metal wire Inside the cylinder. The two electrodes are 
separated by low pressure gas, and the whole is enclosed 
by a glass envelope. A potential difference of 1500-2000 
volts is maintained between the two electrodes. This po- 
tential is only slightly below that required for a spark 
discharge through the gas between the electrodes, A thin 
“window” in the glass permits the entrance of alpha, beta, 
or gamma rays into the chamber. When a particle enters 
the chamber, a quantity of ions is produced in the gas. 
Thus the gas becomes electrically conducting and a dis- 
charge occurs between the two electrodes. 
Fig, 19 Gold Leaf Electroscope 
(a) uncharged (b) charged (c) 
neutralization of charge. 
31 This discharge causes a momentary flow of current 
in the external circuit. The current soon stops, however, 
as the external circuit is so arranged that the external 
voltage is reduced during the discharge. The external 
current may be amplified to cause a ‘click” in a loud 
speaker, to operate a mechanical register, or to cause a 
visual pulse on an oscilloscope screen. 
The Geiger Counter is very useful for studying 
nuclear reactions and can be constructed with such sensi- 
tivity that a single alpha, beta, or gamma emanation may 
be detected and counted. By placing various screens in 
front of the chamber window, it is possible to filter out 
all particles other than the type in which the observer is 
interested. 
Fig* 20 Geiger Counter 
Radioactive Decay 
The decay of radioactive elements such as radium 
into other elements is an example of what is called a 
“statistical process,” which means that me numoer of par- 
ticles undergoing a particular process or reaction is pro- 
portional to the total number of such.' particles present. 
Such processes can also be called probability processes. 
A common example with which we are all familiar is the 
rise or fall of a population. If the excess of births over 
deaths in a given community is forty per thousand, then in 
a population of one thousand people, we expect an increase of 
forty in a year, while if the population is two thousand, the in- 
crease will be twice as great or eighty in a year. Another way 
of expressing this state of affairs would be to say that the pop 
32 ulation is doubling itself every twenty years. Similar relations 
can be derived if the population is decreasing, rather than in- 
creasing. 
The decay of radioactive elements is analogous to a 
population decrease. Radium decays at such a rate that 
the amount of radium halves itself in about sixteen hundred 
years. Thus, if we start with a gram of radium, in 1600 
years we will have only a half _gram left. In 1600 years 
more, a half of that which remained will decay, and we 
will have only a quarter of a gram left. We define the 
decay time or half life of a radioactive element as that 
time required for a given quantity to decompose so that 
only half of it remains. 
It is important to remember the following points - 
the decay time is independent of the amount of material 
present, as long as there are a large number of atoms; 
and the decay time has a constant value for any particular 
element ( or isotope ). The half-life varies greatly for 
different radioactive elements. Thus the half-life of ur- 
anium U238 is several billion years, while that for some 
of the intermediate pr.oducts in its decay to radium and 
thence to lead, is only a millionth of a second. Obviously, 
an element with a large decay time or long half-life is 
more stable than one with a shorter half-life. 
The graph in figure 21 
shows the amounts of radium, 
starting with one gram, that 
remain at various times. No- 
tice that the total amount of 
material which has changed, 
or the rate of change, is much 
higher at the top of the curve 
than at the botton. Theoreti- 
cally the amount of unchanged 
material can never fall to 
zero, although we can say for 
practical purposes, that all of 
the material has disappeared when the amount present is 
less than a measurable quantity. Later we will discuss a 
new element, plutonium (Pu), which was discovered in re- 
cent years as a result of the work on the atomic bomb. 
The half-life of Pu is only 25,000 years. Hence if there 
was an appreciable amount of the element present when 
the earth was formed several billion years ago, it would 
have decayed to such an extent that the amount of it pre- 
sent today would be negligible. Therefore for practical 
purposes, we can say that no Pu exists in nature 
Fig. 21 Radioactive Decay Curve 
33 A rather unusual fact concerning the decay time of 
a radioactive substance Is Its Independence of temperature, 
pressure, presence of catalysts, or other factors which 
Influence chemical reactions. All evidence so far obser- 
ved Indicates that the decay time Is absolutely constant 
for any particular element or Isotope. 
Nuclear Transformations 
In the first section we said that atoms are the smal- 
lest particles which could exist and yet retain the char- 
acteristic properties of the element which they compose. 
We also stated that atoms cannot be destroyed by any 
chemical means. The decomposition of radioactive mater- 
ials Is therefore a new phenomenon to us, and something 
beyond the realm of ordinary chemical changes. For 
example radium (Ra ) Is a very heavy metal, chemically 
active, and In. Its chemical properties greatly resembles 
the rather common element calcium. It has an at. wt. of 
226, and at. no. of 88. But radium decomposes Into an 
entirely different element - radon (Rn), at. wt. 222, at. no. 
86. Radon Is a heavy gas, chemically Inert, and resemb- 
les the gas neon (Ne). Here, we have before us an ex- 
ample of nuclear transformation - one element being con- 
verted Into an entirely different one. Although this trans- 
formation Is Initiated and carried out without our aid or 
control, It nevertheless presents a fascinating possibility. 
Since we now know that the atom Is not Indestructible, and 
that one atom can be changed to another, we visualize the 
possibility of converting one element to another at will, 
and possibly even manufacturing new elements, unheard of 
In nature. The alchemists’ dream may come true, and we 
may yet be able to make gold from lead. Let us see what 
tools will be needed for our work. 
We have two alternatives In changing the nucleus. *We 
may attempt to Increase the atomic number and mass by 
adding particles to It, or we may decrease them by re- 
moving particles from the nucleus. How can this be done? 
Not by any chemical means yet known. We must work 
with the ultimate nuclear particles themselves. With such 
ideas In mind, the physicists of forty ago began 
bombarding various nuclei with alpha particles, electrons, 
and gamma rays from natural sources. Later they also 
employed other nuclear particles - protons, deuterons, and 
so forth - as these became available from artificial 
sources. 
At last, one experiment was successful, and Ruther- 
ford In 1919, found that by bombarding nitrogen with fast 
moving alpha particles he could produce oxygen- These 
34 alpha particles were obtained from disintegrating radium. 
We represent the transformation as follows— 
r^14 + g He4 = 3O17 + 1H1 
The subscripts represent the atomic numbers or nuclear 
charges, and the superscripts the atomic weights. Notice 
that the totals on each side of the equation for both atomic 
numbers and atomic weights must balance. If we consult 
the periodic table of elements, we find that oxygen Is list- 
ed with an atomic weight of only 16, while the oxygen ab- 
ove has an atomic weight of 17. Thus the transformation 
we have produces a heavy Isotope of oxygen, a stable mat- 
erial found In small quantities ( 0.04% ) in the ordinary 
oxygen of the air. 
The amount of heavy oxygen produced by this reac- 
tion Is very small. In fact, the amounts of material pro- 
duced by any kind of nuclear transformations up to the 
recent atomic bomb work were very small, too small to 
be observed by direct weighing. The reader Is then for- 
ced to ask, how did Rutherford know what he'had done 
when he bombarded nitrogen? 
The Wilson C loud Chamber 
To answer the above question we will explain the 
operation of one of the most useful machines known to the 
nuclear physicist for carrying out experiments and Inter- 
preting his results. This Instrument, the Wilson Cloud 
Chamber, Is very simple In principle and operation 
(figure 22). The chamber consists of a cylinder fitted 
with a movable piston which encloses air or other gas. A 
little water In the bottom of the'Cylinder saturates the air 
with water vapor. 
Now if the piston is moved 
downward quickly, causing an 
expansion of the air in the cy- 
linder, the air will be cooled 
slightly. This is a phenomen- 
on familiar to everyone who 
has noticed that the air rush- 
ing out of an automobile tube 
cools the valve through which 
it passes. Since the amount 
of water vapor which can be 
held in the air decreases with 
lowered temperature, the cooled air, which was formerly 
saturated, is now “super-saturated” with water - it is 
holding more water vapor than it should. In other words, 
Fig. 22 Wilson Cloud Chamber 
35 the relative humidity is greater than 100%. However, it is 
possible for this water to stay in the air as vapor for a 
considerable time, unless there are little centers - dust 
particles or ions - on which it can begin to condense out. 
The necessity of such condensation centers, and the fact 
that dust or smoke particles can supply them, explain the 
extensive fogs which are common over such industrial 
cities as Pittsburgh. 
Let us expand the air in the chamber by releasing the 
pressure on the piston. A fog forms since there are 
sufficient dust particles in the air of the-' chamber to act 
as condensation centers. When the fog settles, most of the 
dust particles fall to the top of the piston which forms the 
bottom of the chamber. We then compress the air and re- 
peat the expansion process, causing additional fog forma- 
tion and the settling of more dust particles. After several 
of these compression-expansion cycles, most of the dust 
particles will have been removed from the chamber air, and 
there will not be enough condensation centers to cause fog 
formation when the air is again expanded. Now, if we 
bring a piece of radium near the thin glass window on the 
side of the chamber, some of the alpha and beta particles 
as well as gamma rays will go through the window and 
will produce ions in the air. The water vapor will con- 
dense out as a fog on these ions, and if we have a trans- 
parent top to the chamber, we will readily see white fog 
tracks on the black background of the piston top. Thus, we 
have an almost direct method of observing the path of a 
charged particle. Notice that we say charged particle. 
Uncharged particles are unable to produce ions and cause 
fog; so that they cannot be directly detected in the chamber. 
This is important when we attempt to follow neutrons in 
the chamber, for neutrons are uncharged. 
Inspection of the tracks which particles make in the 
cloud chamber gives us considerable information about 
their nature, and facilitates the identification of unknown 
particles. Figures 23 and 24 are schematic representa- 
tions of cloud chamber tracks of the particles given off by 
decomposition of radium. The short, heavy tracks are 
made by alpha particles, which have a low velocity and 
hence travel only a short distance before dissipating their 
energy. The tracks are thick because a great number of 
ions per centimeter of path are produced by the alpha par- 
ticles. 
The lighter and faster moving beta particles travel 
farther before losing their energy, and therefore have 
longer tracks. Also, since they do not produce so many 
ions per centimeter of path length, their tracks are thinner. 
36 Fig* 23 Cloud Chamber Tracks 
of Alpha Particles. 
Fig. 2U Cloud Chamber Tracks 
of Beta Particles. (Tracks 
curved by magnetic field not 
shown) 
Notice that the tracks of both particles are practically 
straight lines until near the ends, where they curve ap- 
preciably. During most of their flight, the particles are 
moving at high velocities, and are not greatly deflected by 
collisions with the atoms of. the gas. However, at the end 
of the flight, when the velocities have been greatly 
further collisions are able to deflect the particles from 
their straight line paths. 
Gamma rays also produce ions and therefore tracks 
in the chamber. However, the mechanism by which this is 
done is different from that by which alpha and beta parti- 
cles produce ionization, and is rather complicated. Suf- 
fice it to say that gamma rays produce many thin, ir- 
regular tracks, which are easily discernible from those of 
the alpha and beta particles. 
We are now ready to repeat mentally Rutherford's 
experiment. It can be done very simply - all we need is 
a cloud chamber and a small source of alpha particles. 
See figure 25 (a). Most of the alpha particles which enter 
the chamber merely ionize the atoms of oxygen or nitrogen 
in the air; however, once in a very great while, one alpha 
particle will collide head on with the nucleus of a nitrogen 
atom, with the results shown pictorially in figure 25 Cb). 
Notice that the thick track of the incoming alpha particle 
forks into two other tracks. The shorter, thicker track is 
37 made by the new oxygen nucleus formed, while the longer, 
thinner one is made by the proton. Since the proton is 
only 1/17th as heavy as the oxygen nucleus, it moves fast- 
er, and makes a longer and thinner track. Conversely, from 
measurements of the length and thickness of the two tracks, 
it is possible to identify the two particles which produce 
them. 
In order to obtain a complete picture of the reaction, 
it is really necessary to take pictures of the tracks with 
two cameras placed at different positions, so that the cor- 
rect angular relation between the Incoming and exit tracks 
can be determined. The angles must be known in order to 
determine the momenta of the different particles. Since 
momentum is the product of mass and velocity, these two 
important quantities can be calculated. 
We stated that only a very small number of the alpha 
particles are successful in producing disintegration. This 
is rather easy to see, when we recall that the atomic dia- 
meter is so much larger than the nuclear diameter, and 
we need a direct hit on the nucleus to produce the trans- 
formation. We remember that in round numbers the atomic 
diameter is 10~8 cm., and the nuclear diameter only 10“ 12 
cm. The nuclear diameter is smaller by a factor of ten 
thousand, and since the areas of circles and spheres in- 
crease as the squares of their diameters, the nucleus pre- 
$nts a target which is only one hundredth millionth (1/100, 
000,000)' as great as that of the atom as a whole. Thus -an 
alpha particle which lands within the atom will have only 
one chance in a hundred million of hitting the nucleus. 
Looking-at the problem another way, we can say that, on 
the average., a hundred million alpha particles will be re- 
quired to hit a particular nucleus, or one alpha particle 
must go through a hundred million atoms before hitting a 
nucleus. Now the alpha particle, as we have seen, loses 
energy in passing through atoms and ionizing them. Be- 
fore it is brought to a total standstill, an alpha particle of 
average energy (about one million electron volts) can ion- 
ize twenty thousand or so atoms. So dividing a hundred 
million by twenty thousand, we get five thousand, which is 
the number of alpha particles needed to assure the col- 
lision with a single nucleus. But even this figure is con- 
servative, for there is a force which tends to prevent the 
collision of the alpha particle and the nucleus. This is 
coulomb repulsion between the charged particle and the 
charged nucleus. And still a third factor enters to reduce 
the probability that the nucleus will disintegrate or trans- 
form, even when it is hit. The fact is that the nuclear 
stability may not be disturbed sufficiently by the entrance 
of the alpha particle to cause any change in the nucleus. 
The nucleus may merely throw out the alpha particle 
38 a|ain. The physicist says that there is a “barrier energy” 
which must be overcome. This barrier energy is some- 
what analagous to the activation energy of the water in the 
crater, which we discussed in 
Section I. 
Thus there are three fac- 
tors which make the probab- 
ility of nuclear transforma- 
tion very small. They are (1) 
small target area of nucleus, 
(2) repulsion of charged par- 
ticle by charged nucleus, and 
(3) barrier energy which must 
be overcome. The combined 
effect of all these factors 
makes the probability of caus- 
ing transformation about one 
for each hundred thousand 
particles used. Hence, of one 
hundred thousand alpha par- 
ticles which are shot at nitro- 
gen atoms, only one is effec- 
tive in causing the nitrogen to 
turn into oxygen, and the others 
are simply wasted. 
Returning to our cloud 
chamber photographs we see 
that a great many photographs 
must be taken before one is 
found which shows the nuclear 
disintegration. In order to 
avoid tediousness, automatic 
photographs may be taken by 
opening the camera, just at 
the instant chamber has ex- 
panded. After this, the cham- 
ber must be compressed 
again and the fog cleared away by applying an electric 
charge to the walls of the chamber. The charge will 
neutralize the ions and draw them to the walls. The 
difficulty -is that the time required to get the chamber rea- 
dy for the entrance of the next particle is about forty 
times as great as the expansion time in the chamber, so 
that the chamber is good for observations only about two 
per cent of the total operating time. Recently, however, 
the cloud chamber has been further modified by use of 
vacuum tube circuits, so that a photograph will be taken 
Fig, 25 Rutherford's Experi- 
ment, 
(a) Simplified Representa- 
tion of Apparatus (b) Simpli- 
fied Representation of Cloud 
Chamber Photographs (c) Ex- 
planation of the Nuclear Tran- 
sformation, 
29 only when a track is produced as a result of a nuclear 
transformation. The instrument may be modified so that 
it will respond only to a particular type of transformation. 
Thus, the time of the experimental observation and the 
amount of photographic film needed may be greatly reduced 
Equivalence of Mass and Energy 
In the previous section we learned that by the bom- 
barding of nitrogen nuclei with high speed alpha particles, 
we are able to transform the nitrogen nucleus into that of 
an isotope of oxygen. Following this discovery by Ruther- 
ford, other physicists got busy and bombarded other ele- 
ments with alpha particles of different speeds or energy 
contents, and with other particles as well. Recalling vhat 
we have learned in the previous sections, we can see that 
we have a choice of several particles. Let us list these 
particles in order to obtain a composite picture of the 
possibilities: 
Particle 
Mass 
..Charge. 
Remarks 
electron 
zero 
practically 
-1 
Same as beta ray 
positron 
1 
Not yet used as bomb- 
arding particles 
proton 
1 
1 
Same as hydrogen ion 
neutron 
1 
0 
Same zero charge, as 
hydrogen atom, approx, 
same,mass, but not at 
all alike in structure 
deuteron 
2 
i 
Same as heavy hydro- 
gen ion 
alpha particle. 
4 
2 
Same as helium ion 
gamma rays... 
0 
0 
Not particles, but 
* ‘bundles’ bof energy 
When these particles are used at various speeds a 
great number of nuclear transformations may be effected. 
It is not necessary for us to go into these various reac- 
tions in detail, but we, can summarize them by saying that 
when one of the particles listed above is shot at a nucleus 
of a particular element or isotope, atomic number can in- 
crease by zero, one,-or two units, or decrease by one unit. 
Mass number can increase by zero, one, two, three, or 
four units. This mdy lead to the formation of an intermediate 
substance. If the intermediate substance is radioactive, it 
will then emit one of the particles listed above, the 
emitted particle generally being different from that of the 
40 original bombarding particle. We speak of gamma rays 
in this sense as if they were the same as any other par- 
ticles, although actually gamma rays are not particles, 
but waves of energy, as we have previously stated. It is 
important to repeat that the change in the nucleus is only 
a few units, either in atomic number or atomic weight. 
We shall later find an important exception to this state- 
ment when uranium is bombarded with neutrons. This 
reaction produces a much greater change in the nucleus. 
In fact the nucleus is practically split in two. This is 
the process known as t‘fission of uranium.” 
Mass Changes in Nuclear Reactions 
Let us consider the reaction of lithium (Li, at. no.3, 
at. wt. 7) bombarded by protons. It has been found that 
Lor each Li atom that reacts, two atoms of helium are 
formed. The equation is: 
3Li? + iH1 = 2 2He4 
If instead of considering one atom of Li, we consider a 
gram mole of its atoms, we find some very interesting 
information by comparing the weights of the reactants 
( Li, H ) and the products. Using the very accurate val- 
ues of atomic weights determined by the modern mass 
spectrograph , we Compile the following weight ballance: 
Mass of Li — 7.01818 gms 
” ” H — 1.00813 
Total mass of reactants 8.02631 
Mass of He — 4.00389 
” ” ” — 4.00389 
Total of mass products 8.00778 gm. 
We immediately, see that the two totals do not balance. In 
fact, there is an excess of 8.02631 minus 8.00778 = 
0.01853 gm, of reactants over products. If our work has 
been conducted carefully and accurately, and there are no 
other particles which account for this mass difference, we 
conclude that this amount of material has been lost or 
destroyed. But this conclusion is a contradiction to our 
common sense, and to the fundamental law of physics and 
chemistry, that matter can neither be created nor destroy 
ed. We had another similar law which stated energy can 
neither be created nor destroyed. Now we are forced to 
revise our ideas somewhat. As Einstein has proved, the 
41 true state of affairs is “The sum of matter and energy In 
a particular system is constant, but matter and energy are 
mutually interconvertible.” Thus Einstein explained that 
the above mass difference was converted into a quantity of 
energy. In this reaction careful experiments showed that 
the helium atoms thrown off from the reaction were mov- 
ing with a considerable velocity (about one twentieth the 
velocity of light), and therefore possessed a great deal of 
kinetic energy. Einstein has furthermore stated that a 
very simple relation exists between mass and energy, ex- 
pressed: 
E * me 2 * km 
Here E is the amount of energy in ergs, m is the mass 
in grams, and k=c2 is a constant equal to 9 x 10*0. 
“c" itself has a value of 3 x which is also the vel- 
ocity of light in cm./sec. Thus, when 0.01853 gm. of 
mass disappear, the equivalent amount of energy, (0.01853) 
x (9x1C)20) = 1.07 x 1019 ergs appears. The erg is a 
rather small unit of energy, so we will convert it into 
units with which we are more familiar. One erg » 9.48 
x 10-Hbtu = 7.38 x 10-8 ft. lb. = 2.77 x 10“l3 kw.hr. 
Converting from ergs to btu, we obtain a value » 1.58 x 
10® btu. If we recall that the burning of a pound of coal 
produces about 15,000 btu, the the burning of a ton will 
produce (2000) x (15,000) = x 10*7 btu. Comparing 
this value with the 1.58 x 10y btu for the nuclear reaction, 
we see that the amount of energy liberated when only 
seven granis of Li combine with one gram of H is equiv- 
alent to that obtained from the burning of about 50 tons of 
coal. Remembering that there are 454 grams to the 
pound, we can show that the reaction with a pound of Li 
would be equivalent to about 3250 tons or seven million 
pounds of coal I This is a huge figure, but it is not un- 
upual for nuclear reactions. In fact it is useful to remember 
mat nuclear reactions can be much greater - even one 
million to one hundred million times as great as the us- 
ual chemical reactions. Ten million times is a good av- 
erage figure to remember. 
The conversion of mass into energy is a concept 
which is very new to most of us, who have always been 
schooled according to classical physics, and thought that 
mass was indestructible, and likewise energy. The in- 
quiring reader will immediately wonder why this conver- 
sion was not previously detected. The reason is that the 
energy changes in the chemical reactions with which we 
were familiar were so much smaller than the nuclear 
energy changes, that the mass differences produced were 
not noticeable. As an example, suppose we heat a 500 
42 gallon tank of water from its freezing point (32° F.) to its 
boiling point (212° F.). Since there are 8.33 pounds to the 
gallon of water, the amount of heat we put into the water, 
is (500) x (8.33) x (212-32) = 750,000 btu. Using the con- 
version factor previously given for btu to ergs, we see 
that this is also equal to 7.5 x 10° -i~ 9.49 x 10"11 = 7.9 
x 10*° ergs. But according to the Einstein equation, one 
gram is equivalent to 9 x 10™ ergs; the mass equivalent 
of our energy input is, therefore, only 7.9 x lO 9 x 
1020 s 0.000009 gm. This is about one hundredth of a 
milligram, and a milligram is the smallest unit accurately 
measured on the ordinary chemical balance.. With a, micro 
balance, the mass difference of 0.000009 gm. can be* dis - 
tinguished in a sample totaling a few milligrams. How- 
ever, it is obviously impossible to measure such a small 
mass (which is far less than that of an average Texas 
mosquito) when it is associated with that of five hundred 
gallons of water. It was not until the huge energy chang- 
es associated with nuclear reactions were discovered, that 
mass changes large enough to be detected were found. 
Predicting Nuclear Reactions 
From a knowledge of the energy contents of various 
elements and chemical compounds, the chemist is able to 
predict possible reactions. In general he is able to say 
that those reactions which liberate energy will go spontan- 
eously, and that those which absorb energy do not go 
spontaneously, but require the addition of energy to make 
them go. Although he uses a term called “free energy,” 
which is somewhat different from ordinary heat of re- 
action, we need not concern ourselves with it at present. 
Of course, this sort of calculation does not predict 
how fast the reaction will go, nor what the yield will be, 
but only whether or not the reaction is possible. We can 
do the same thing with nuclear reactions. AH we need do 
is write down an equation, properly balanced, and write 
the proper atomic masses below, as we did in the Li-H 
reaction. Then, if the sum of the masses of the products 
is less than the sum of the masses of the reactants, there 
will be a liberation of energy and the reaction is pro- 
bable. On the other hand, if the sum of the masses of 
the products is greater than that of the reactants, energy 
must be added to cause the reaction. We repeat that the 
most probable reactions are those which liberate energy. 
Now, since we know that all nuclei are .composed of 
the two basic partices, the proton and neutron, in varying 
numbers, it is interesting to compare the mass of the 
nucleus with that of its component parts. If the nuclear 
mass is less than that of the “free” protons and neutrons 
43 wMcn compose It, then the nucleus Is stable; conversely if 
the nuclear mass is greater than that of its component 
parts, the nucleus is unstable. If the nucleus is unstable, 
the amount of instability energy will be directly propor- 
tional to the amount of mass excess, and it will tend to 
break down into more stable nuclei, or to build up into 
more stable nuclei, as the case may be. 
Fig. 26 Relation of Packing Fraction to Mass Number. 
The Packing Fraction 
In order to have a convenient scale for measuring 
nuclear stability, we make use of a curve known as the 
packing fraction curve (figure 26). The curve has as its 
base oxygen, which has an atomic weight of 16.0000, and 
a mass number (number of protons and neutrons in the 
nucleus) of 16 . Ail other elements have an integral mass 
number, but their atomic weights are either a little great- 
er or a little less than this integral number. Thus the 
mass number of hydrogen is one, while its atomic weight 
is 1.00778. We define the packing fraction as the differ- 
ence between the atomic weight and the mass number, 
divided by the mass number and multiplied by ten thou- 
sand. Thus for hydrogen the packing fraction is 
1.00778 - 1.00000 
X 10,000 = 77.8. 
1 
For He, atomic weight 4.00216, mass number four, the 
packing fraction is 
4.00216 — 4.00000 
X 10,000 * 5.4 
4 
44 Notice that the packing fraction for He is considerably less 
than that for hydrogen, which means that He is more 
stable than H. We might consider as a source of energy 
the building of heavier He nuclei from lighter hydrogen 
nuclei. Let us calculate the energy which we can theo- 
retically obtain per mole of He formed. 
The He nucleus is composed of two neutrons and two 
protons. 
Wt. of neutrons 
2 ( 1.00897 ) = 2.01794 
Wt. of protons 
Z ( 1.00778 ) = 2.01556 
Total wt. of nucleons .... 4.03350 
Wt. of He nuclei 4.00216 
Mass loss for reaction . . 0.023134 gm. 
We see that for each four grams of He produced there is 
a loss of 0.031 gm. Converting this mass loss to an 
energy production, we obtain about 2.8 X 1019 ergs or 2.7 
X IQ® btu. 
We have dealt at length with this particular reaction 
because it is probably the most important one known. 
This is the reaction by which the sun produces its energy. 
The sun is continually converting its hydrogen into helium 
and producing heat at the rate of 3.78 X 1(533 ergs per 
second. This corresponds to a mass loss of nearly five 
million tons per second. The amount of the sun's energy 
which the earth receives is so small, however, that it 
corresponds to a mass ’increase of the earth of only 150 
tons per day. The vastness of the sun can be realized 
when we consider that it is over a billion years old, and 
had not used up more than one-tenth the hydrogen which it 
had a billion years ago. 
Lest the reader become over-enthusiastic about the 
possibilities of producing energy by nuclear reations, we 
must repeat that such calculations which we have just car- 
ried out for the hydrogen-helium conversion show only the 
possibility of the reaction, not the speed or conditions 
under which it will take place. 
Actually it is necessary to maintain a temperature of 
about twenty minion degrees, as exists in the sun's in- 
terior, in order for this reaction to occur. Neither is 
45 
780893 ()—48 4 the reaction as simple as we have supposed it, but goes 
in a complex, step-wise manner, involving several inter- 
mediate, unstable elements. A possible explanation of 
this complicated reaction is given Dy figure 27. 
Thermonuclear Reactions 
We may predict the direc- 
tion or possibility of a given 
reaction’s occuring as we 
have just seen, merely from 
correct values of the masses 
of the elements involved. How- 
ever, the rates of sueh reac- 
tions, even as those for chem- 
ical reactions, are influenced 
by the activation energies for 
the reactions. The concept of 
activation energy was discus- 
sed in Section I. If the activa- 
tion energy of a reaction is 
high, a high temperature is 
required to make the reaction 
go; conversely, low temper- 
atures are sufficient to initiate low activation energy re- 
actions. The effect of temperature can be seen by consid- 
figure 28. The accompanying curves, known as Max- 
well distribution curves, give at any temperature the num- 
ber of atoms possessing given energy values. 
Fig. 27 The Carbon Cycle by 
which the Sun Produces its 
energy. 
In the first section, when we discussed kinetic theory 
of gases we assumed that all of the molecules of a gas are 
moving at the same velocity and have the same energy. 
This assumption is not true. Actually a small number have 
low energies, and a small number much higher energies 
than the average. It is only those molecules (or in the 
case of nuclear reactions-atoms) which have energies a- 
bove a certain value in excess of the average, that are able 
to react. This excess above the average energy is the 
same as the term we have called the activation energy. 
As we increase the temperature of the mass of the sub- 
stance, all of the molecules or atoms are speeded up and 
their energies increased. We then have more molecules 
which possess energies in excess of the required activa- 
tional energy and are thus able to react. Therefore, the 
reaction rate increased with temperature. With ordinary 
chemical reactions, the activation energies are of the order 
of 10,000 - 40,000 calories per mole and chemical react- 
ion rates usually double for each ten degree rise in tem- 
perature. 
46 Referring to Figure 28 we 
see that at the low tempera- 
ture there are atoms hav- 
ing an energy equal to the 
activational energy. All atoms 
having this energy or a higher 
energy (those atoms to the 
right of the dashed vertical 
line) are then able to react. 
The total number of such high 
energy atoms is represented 
by the area between the low 
temperature curve and the 
horizontal axis. At higher 
temperature it will be noticed 
that an additional number of 
atoms are available; thus the area between the high tem- 
perature curve and the horizontal axis is about twice that 
between the axis and the low temperature curve, and the 
reaction will be about twice as fast. 
However, for nuclear reactions, the activational ener- 
gies are of the order of millions of calories, and the tem- 
perature effect is much more pronounced. Thus it is nec- 
essary to resort to much higher temperatures to cause the 
nuclear reactions to take place at appreciable rates. These 
temperatures are so high that nuclear reactions initiated 
by purely thermal means are impracticable in most cases. 
Usually we must resort to fast-moving nuclear particles 
for accomplishing our taks. Figure 29 shows the effect of 
temperature on a typical nuclear reaction. 
Nuclear Fission 
In figure 26 , one notices 
that the packing fraction de- 
creases as we increase the 
mass number - from a high 
value at hydrogen to minimum 
values for intermediate mass 
numbers. It then increases 
again as we reach the high end 
of the periodic table. Since 
the minimum values of thd' 
packing fraction indicate in- 
creased stability, we see that 
light elements of low mass 
number can be stabilized 
Fig# 28 Maxwell Distribution 
Curves for Atoms at Different 
Temperatures. 
Fig. 29 Effect of Temperature 
on Thermonuclear Reactions. 
47 In figure 26, one notices that the packing fraction de- 
creases as we increase the mass number - from a high 
value at hydrogen to minimum values for intermediate 
mass numbers. It then increases again as we reach the 
high end of the periodic table. Since the minimum values 
of the packing fraction Indicate increased stability, we see 
that light elements of low mass number can be stabilized 
by fusion to form elements in the middle of the periodic 
table. Likewise, heavy elements can be stabilized by 
fission into elements in the middle of the table. The 
atomic bomb utilizes the latter principle. Notice that the 
packing fraction of uranium is the highest of the natural 
elements on the heavy end of the table; thus it will be the 
most unstable element in respect to fission. Fortunately, 
its activational energy is very low, so that the fission of 
uranium is not only theoretically possible, but also highly 
probable. U235 has an even higher instability and lower 
activation energy, than does the abundant isotope. 
It is for this reason that U235 is the material we are 
mainly interested in for utilization of atomic energy - 
either for military or peacetime purposes. We will dis- 
cuss later a new element, plutonium (Pu) which is also 
attractive from this standpoint. 
48  
SUMMARY OF REACTION 
TYPES 
Reaction 
, Type 
Normal Mass Change 
Dependence on Energy 
of Projectile 
Yield 
Type of Radioactivity 
Usually Produced 
Sample Reactions 
ncapture 
Positive 
Resonance 
Virtually 100% 
Electron 
Agior 4- n -r*Agi°8 
Br79 4* n —*Br80 
np 
Slightly positive 
Smooth 
Large for light elements; 
escaping barrier to 
consider 
Electron 
N'« + w -*C4 + 
S82 + n -*P82+Hi 
n a 
Slightly positive in light 
elements; negative in 
Smooth 
As above 
Electron 
F'9 + n —t-N18 + He4 
Al27 + n -t-Na^+He4 
n, 2n 
Very negative 
Smooth 
Small 
Positron 
N1* + n —*N18 + 2n 
pn + „ —+ p>o + 2 n 
p capture 
Positive 
Resonance 
Large 
Positron 
C12 -f- Hi -+N18 
F19 + Hi —*Ne20 
pn 
Negative 
Threshold; smooth 
increasing with energy 
Large 
Positron 
B11 + Hi -*C” + n 
Oi8 + Hi -4-Fis + n 
Vet 
Slightly positive in light 
elements; negative in 
heavy 
Smooth, Increasing with 
proton energy 
Large 
Generally stable products 
F19 + Hi -+• Oi* + He4 
Al27 + Hi -+ Mg24 + He4 
pd 
Very negative 
Smooth as above 
Small 
Only one case established 
Be9 -f Hi —+ Be8 + H2 
an 
Slightly negative in light 
elements; positive in 
heavy 
Smooth 
Large for elements where 
barrier penetration is 
easy 
Positron 
Bio -J- He4 ► N18 + » 
Al27 + He4 —► P80 +w 
aP 
Slightly positive except 
some light elements 
Smooth 
As above 
Generally stable products 
Al27 + He4-* Si" + Hi 
N14 + He4 —* Oi7 +Hi 
dp 
Always positive 
Smooth 
As above 
Electron 
Na28 + H2 -*Na24 + Hi 
psi + h2 -*P82 + Hi 
dn 
As above 
Smooth 
As above 
Positron 
C'2 + H2 -*Ni8 + Hi 
Be9 + H2 -* Bio + hi 
d CL 
Always positive 
Smooth 
As above 
Generally stable products 
©is + H2 —* N'4 + He4 
Al27 -f H2 -* Mg25 + He4 
r« 
Always negative 
Sharp threshold 
Small 
Positron 
Be9 + T —*Be8 +n 
Br8i + r -*Br*° + n 
r v 
As above 
As above 
As above 
Only observed for 
deuteron 
H2 + T -*« + H1 
Fig. 30 FISSION OF URANIUM 
THE MANHATTAN DISTRICT 
Nuclear Bombardment with Neutrons 
In Section IV we saw how the various nuclear 
particles - alpha particles, protons, deuterons - may be 
used as “bullets” for bombarding atomic nuclei to pro- 
duce transmution. We saw that one of the main difficul- 
ties in hitting the nucleus is the electrical repulsion be- 
tween the positively charged nucleus and the positively 
charged bombarding particle. However, we could avoid 
this difficulty by using a stream of neutrons as the bomb- 
arding particles, and we should expect neutrons to be very 
effective bullets for nuclear transformations. This is act- 
ually the case. However, we are seriously limited in our 
use of neutrons by the fact that we do not have any natur- 
al source of neutrons available. We have shown that we 
can produce streams of protons, deuterons, and alpha par- 
ticles in considerable quantities, by merely ionizing hydro- 
gen, deuterium, or helium. However, to obtain neutrons 
we must rely on some other nuclear reaction, such as that 
between alpha particles and beryllium or between deuter- 
ons and deuterium. Since these reactions themselves are 
slowed by the electrical repulsion between the nuclei and 
bombarding particles, we are back where we started. 
Suppose, however, that we were able to find a react- 
ion initiated by bombarding neutrons and giving neutrons as 
a reaction product. If the reaction gave only one neutron 
for each atom which reacted, it would continue at a fixed 
rate until all the material in the reacting mass had been 
used up. But if the reaction gave more than one, say two, 
neutrons for each reacting atom, then after the first atom 
had reacted, we would have two available neutrons. These 
could then react with two more atoms, to produce four re- 
actions; these four reacting atoms would give eight neut- 
rons, and so on. Thus the reaction rate would increase 
very rapidly. If the energy of such a reaction were be- 
ing produced faster than it could be dissipated to its sur- 
roundings, we would have an explosion. 
A reaction such as we have postulated is known as a 
“branching chain reaction,” of which we have many ex- 
50 amples in chemistry, The addition of -an electric spark, 
to a mixture of hydrogen and oxygen gases supplies suff- 
icient activation energy to cause the reaction of a few 
atoms in the neighborhood of the spark. These atoms. 
Fig. 31 Production of Neutrons by a Branching 
Chain Reaction, 
combining to form HgO, generate heat, and this heat is ab 
sorbed by more atoms to satisfy their activational energy 
requirements, causing them to combine, and so on. Thus 
the entire hydrogen-oxygen mass quickly reacts. If the 
gases are confined so that they build up a pressure and 
cannot otherwise dissipate their energy, an explosion re- 
sults. We shall see shortly that such a branching chain 
reaction is not only possible, but actually occurs in the 
decomposition of uranium nuclei under certain conditions. 
Uranium Fission 
If the reader will scan over the various examples of nu- 
clear reactions which he studied in the fifth section, he will 
notice that in no case was any particle heavier than an alpha 
particle emitted from the nucleus. During the 1930’s var- 
ious. workers in the field of nuclear physics bombarded 
uranium with the neutrons and found that tremendous ener- 
gies were given off by the reaction. The energy output was 
of the order of 200 Mev per nucleus re-acting, while the us- 
51 ual nuclear reactions involved energy changes of only a few 
Mev, usually less than ten. Such huge energy outputs prom- 
pted considerable research as physicists were naturally in- 
terested in obtaining these great amounts of energy in suffic- 
ient quantities to be practical in industry. At this time the 
exact nature of the reaction was not known, since the actual 
amount of reacting material was too small to be weighed or 
efficiently investigated. 
Various theories were propounded as to the products 
of the reaction, the prevailing theory being that the neut- 
ron had been captured by the uranium nucleus to yield 
elements of higher atomic number than uranium,, In fact, 
if one looks at the periodic chemical tables published dur- 
ing the late ‘30s, he will notice the presence of elements 
No. 93, 94, etc. The exact nature of the process was re- 
vealed by the German and Strassmann. By 
use of tracer chemistry, they showed that the uranium was 
producing barium, krypton, and several other elements in 
the middle of the periodic table. These elements have 
about half the atomic weight of uranium. Dr. Lise Meitner 
then postulated that these materials were formed by the 
splitting of the uranium neucleus into two approximately 
equal parts. Here was the first example of fission of a 
heavy nucleus. Subsequent work has shown that the fis- 
sion of uranium also produces several neutrons. The exact 
number of neutrons produced per fission can not be re- 
vealed for security reasons. It can be assumed to be 
between two and three on the average. In our future dis- 
•cusslons we will consider the number to be two for sim- 
plicity. 
A word here about tracer chemistry, which is a very 
useful tool both to the physicist and to the biologist. Sup- 
pose we attempt to identify the products of the uranium- 
neutron reaction. Let us mix the small amount of the pro- 
ducts with" a quantity of a barium salt solution in water, and 
then precipitate the barium by addition of a sulphate to the 
solution. The barium will be precipitated as the insoluble bar- 
ium sulphate. It will be found that the radioactivity associated 
with the unknown material is in the precipitate and not in the 
remaining solution. This suggests that the unknown material 
was itself a radioactive form of barium, and because of its 
similarity to barium in chemical properties, it precipitated 
with the normal barium. If we use materials which give pre- 
cipitates of silver, zinc or copper instead of barium, we find 
no radioactivity in the precipitates, and thus the unknown pro- 
duct does not contain these elements. By such experiments as 
these Hahn was able to identify the materials which were pro- 
duced by the action of neutrons on uranium. 
It will be useful for us to investigate more closely 
the mechanism of uranium fission. If we look again at 
52 figure lb, which gives the activational energies for fission 
of the various elements, we see that the values are rather 
high until we reach the very heavy elements of the per- 
iodic table. Thus an activation energy of about 50 Mev 
must be supplieb for the fission of tin. Since this is a 
much higher energy than that of any neutrons which we can 
obtain at present, we cannot expect tin to be fissionable by 
neutrons. As we go up the table, to terbium (Tb) for in- 
stance, we find an activational energy of about 20 Mev. 
But even if we were able to produce 20 Mev neutrons, we 
wbuld not have a self-sustaining fission reaction in Tb be- 
cause the fission does not produce more neutrons of this 
energy. The neutrons produced by fission of Tb have 
energies of only one to two Mev. 
Fig. 32 Energy Barrier and Barrier Leakage Effect, 
When we reach Thorium and Ugss, we see that the act- 
ivational energies are even lower, only about 5 Mev, and 
we find that it is possible to produce fission with neutrons 
of only one Mev energy. This is possible because neutrons 
need not possess energies as high as the activational en- 
ergy in order to penetrate the potential energy barrier of 
the nucleus. According to the quantum theory, as postula- 
ted by Gamow et.al., there is .a certain probability of less 
energetic neutrons leaking” through the energy barrier 
and getting into the nucleus. This probability increases 
from a very small value for low energy neutrons to a 
value of 100% for those having energies as high as the 
53 fission activational energy. This concept of barrier leak- 
age is rather difficult to understand, but we must ask the 
reader to accept it on faith, and leave the job of explain- 
ing it to the quantum mechanics workers. Figure 36 
illustrates the effect of incoming neutron velocity on bar- 
rier penetration and leakage. 
Thus when we come to Thorium we find that neutrons 
of only one Mev energy are able to produce fission of the 
thorium nucleus. In fact, of every twenty five neutrons 
which get inside the Thorium nucleus, about one will 
cause fission. The other twenty-four are kicked out of the 
nucleus again, at a lower energy than that with which they 
entered. This is because the activation energy for re- 
emission of the neutron is less than that for fission of 
the nucleus, so that the re-emission process is more like- 
ly to occur than is fission. The reason that the re- 
emitted neutron is less energetic than the entering one is 
that it has distributed a considerable amount of its energy 
to the other particles in the nucleus, causing them to vi- 
brate until they have dissipated this normal energy by 
emission of gamma rays, and returned to their normal 
state. The neutron before leaking through the barrier 
need have* only a slightly larger amount of energy than 
that required for re-emission. This value for re-emis- 
sion is about 5 Mev for all nuclei. In leaking through the 
barrier the neutron uses up 5 Mev and then has practic- 
ally no energy left. 
When we reach Uooo, the activational energy for fis- 
sion is still less, and of every five neutrons getting into 
the nucleus, one is able to produce fission. This is still 
not good enough to give us a self-sustaining reaction. 
Each fission gives two more neutrons, so that we have 
received only two neutrons for the five we put in. But 
for U23R, the rarer isotope of uranium, the fission act- 
ivationai energy is less than five Mev (the re-emission 
activational energy), and fission is more probable than 
re-emission of the neutron. We now have a probability 
of better than one out of two neutrons producing fission, 
and since each nucleus undergoing fission gives rise to 
two more neutrons, we will get out more neutrons than 
we put in, and a sulf-sustaining reaction is possible. 
With the elements Neptunium (Np) and Plutonium (Pu), 
which we shall discuss later, the same situation holds, 
and fission by a self-sustaining chain reaction is possible. 
We shall see that Pu is satisfactory as a source of the 
chain reaction, but that Np cannot be used because of 
practical difficulties, the chief one of which is its short 
half-life. 
54 We have mentioned U235 and Qgoo 111 above 
paragraph. These are two isotopes of uranium. In any 
natural source the heavier U938 composes about 99.3% 
of the total, and the lighter 0335 about 0.7% of the total. 
There is a third isotope, U234, but its proportion is less 
than 0.1% and we will not be concerned with it. Work 
subsequent to that of Hahn, Meitner, et. al. showed that 
fission of uranium by neutrons was mainly fission of U235, 
and that the effect of U23 q was niainly as a diluent, or 
something which slowed down the reaction. 
We can understand this diluting action of the U238 by 
recalling that we get out only two neutrons for every live 
we put in. Since the amount of Uggg is about 140 times 
as great as that of it is very probable that most of 
the neutrons given on by the fissioning U235 will be cap- 
tured by the U938 rather than by more U935, and these 
will mainly be lost. Thus we cannot produce a self-sus- 
taining chain reaction in a natural source of uranium, al- 
though we can easily do so in pure U235, and possibly in 
a material which contains more U235 than a natural 
source, that is an “enriched” source. 
We have now reached in our discussion the state of 
affairs existing in 1939, when Professor Einstein wrote to 
President Roosevelt suggesting that intensive research 
work be carried on to investigate the possibilities of us- 
ing the fission of U935 i32 a branching chain reaction as 
a source of energy for military application. Subsequent- 
ly the Manhattan District was organized with plants at 
Oak Ridge, Tennessee, and laboratores at many educa- 
tional institutions throughout the country. One of the 
more important of these laboratories was the so-called 
“Metallurgical Laboratory’’ at the University of Chicago. 
Work of the Manhattan District 
Let us now briefly restate the problem which faced 
the Manhattan District. We know that uranium is fission- 
able by neutrons with the liberation of tremendous quan- 
tities of energy. We also know that if this energy can be 
liberated in a very short time, we can produce a power- 
ful explosion of great military value. But this explosion 
will only be possible if we are able to split uranium in a 
branching chain reaction. Such a branching chain react- 
ion is possible in Pure U235, or 311 enriched uranium 
source, but not in natural sources containing both U235 
and U238. The problem, then, is to find a way of en- 
riching natural uranium sources, so as to give a* rela- 
tively pure source of U235. The obvious solution to the problem is to separate 
the two isotopes of uranium, since we can then have our 
pure source of U235. However, this separation is a 
difficult task. We have already learned that isotopbs 
have identical chemical properties, and thus cannot be 
separated by chemical means. We will have to resort to 
physical methods of separation, which will be difficult arid 
tedious because of the slight differences in the atomic 
weights of the isotopes, 235 and 238. Several different 
methods of separation were investigated, both from theo- 
retical and practical aspects, and two of these methods 
were put into large scale application. We shall briefly 
discuss these various methods. The two methods which 
were finally put into operation required the fabrication of 
large industrial plants. 
A. Centrifuge Method 
The centrifuge separation employs a principle with 
which wre are all familiar. A common example is the 
separation of the lighter cream from the heavier bulk of 
the milk. Its principle is merely that liquids or gases of 
different densities, under the influence of gravity or a 
force similar to it, will “settle out” into layers corres- 
ponding to their densities. With gravity alone, the settl- 
ing is usually very slow, so that a centrifuge is employed 
to speed up the process. The centrifugal force is the 
force on a particle moving in a circular or other curved 
path, and tending to throw the particle out from the center. 
The force is directly proportional the the mass of the 
particle and to the square of its velocity, and inversely 
proportional to the radius of the circular path in which it 
is moving. It will therefore tend to throw out heavy (den- 
se) particles farther than light ones, and thus will accom- 
plish a separation according to densities, lust as gravity 
does by settling. Since the force increases rapidly with 
the velocity of the moving particle, this means that the 
rotors of the centrifuge should be moving very rapidly, 
and they should be of small diameter or radius, since the 
centrifugal force increases when the radius decreases. By 
use of high speed centrifuges, it is possible to obtain for- 
ces more than a million times stronger than those of gra- 
vity. 
The centrifugal force on particles moving with a 
given speed along a path of given radius is proportional 
to their mass. Therefore the difference in the force for 
two particles of different masses will be proportional to 
their mass differences, or to the difference in densities 
for the bulk materials. This is not in contradiction to 
anything we already know. We know that it is much eas- 
ier to separate oil (density 0.8 gms./cc) from water 
56 Cl.00 gms./cc), than It is to separate milk (1.03) from 
cream (0.97). Since gas densities are so much less than 
liquid densities, the differences in densities between gas- 
es are very small, and very great centrifugal forces are 
needed. Furthermore, the continuous, rapid motion of 
gaseous molecules in all directions hinders the separation 
and necessitates the use of very complicated and expen- 
sive equipment. 
For separation of the uranium isotopes, the uranium 
was converted into the compounds Ij235 pg, and xj238 Fg, 
of molecular weights 339 and 342.' Although the fluoride, 
because of its chemical activity, is a difficult material to 
handle, it is one of the few compounds which is theoreti- 
cally suitable. Its virtue lies in the fact that fluorine is 
one of the few elements which have no stable isotopes, 
only the normal Fi9 is stable. The ratio of densities of 
gases is proportional to the ratio of their molecular wei- 
ghts, and the size of this ratio is a measure of the ease 
of separation. Thus the ratio for the two fluorides of IJ238 
and U235 is 342/339 = 1.009. This is not a very large 
ratio. In fact, if the ratio were 1.000C), no separation 
would be possible. Compare this ratio with that for oil 
and water, 1.00/0.80 = 1.250. 
The low separation factor indicates to us that the 
separation will be difficult. Observations and calculations 
made by the in the Manhattan Project indicated 
that to produce only one kilogram (2.2Ilbs. ) per day of 
U235 would require 22,000 separately driven high-speed 
centrifuges. These figures are quite impractical, and 
thus the centrifuge method of separation was abandoned. 
B. Diffusion Methods of Separation 
The principle of diffusion methods of separation takes 
us back to the kinetic theory of gases. We recall that all 
of the molecules of a gas at a given temperature have the 
same average kinetic energy. This kinetic energy is equal 
to one half the product of the molecular mass and the 
square of its velocity. Thus for molecules of varying 
mass at the same temperature, we may write 
E, = Ea 
1 = 1 
Ymiv/ 
mj y,* Vj fm* 
mz Vvi ' mi 
57 Thus the molecular velocities of the different gases 
at the same temperature are inversely proportional to the 
square root of their molecular weights. The rate with 
which the molecules, in the gaseous state, diffuse through 
a porous membrane is proportional to their absolute mole- 
cular velocities. This means that if a quantity of a gas 
containing light and heavy molecules is allowed to diffuse 
into an evacuated space through a porous membrane, the 
light molecules will move through more quickly than the 
heavy ones. That part which goes through the membrane 
will then have a greater proportion of the lighter, fast 
moving molecules, and that part remaining behind will have 
a greater proportion of the heavier, slowly moving ones. 
The ratio of the molecular velocities will be a mea- 
sure of the ease of separation, and a low separation fac- 
tor means that many stages, or individual membranes 
must be used to effect any appreciable differences in con- 
centration. This ratio will be 
[342 
M539 = 1-0044> 
which is even smaller than the separation factor for centri 
fuging. The factor of 1.0044 is a theoretical factor to be 
used for a -process which does very little actual separa- 
tion. In other words it is only for the first small frac- 
tion of the gas which comes through the barrier. If any 
appreciable material is to be gathered, the factor falls off. 
It will naturally be 1.0000 if all of the material goes 
through the membrane, since there will then be no separa- 
tion. We might take 1.003 as a working factor. 
Despite this low separation factor, the gaseous dif- 
fusion process proved the best process for large scale pro- 
duction of U235. 
Many practical difficulties had to be solved, and a 
few may be mentioned here. 
The material UFg, is a “bad actor/* Upon Contact 
with traces of water vapor it forms the very corrosive 
hydrofluoric acid. In addition it is a solid at room tem- 
peratures, and presents difficulties of “freezing’* in the 
lines, etc. Thus the handling of UFg presents many eng- 
ineering problems. 
Because of the small enrichment factor of the dif- 
fusion separation, large quantities of gas and large areas 
of barrier or membrane material are required. This 
means a great deal of equipment is necessary. The pro- 
blem of recycling the gas through the stages must also be 
58 considered. If we suppose that we push only one half of 
the gas from any one stage to the next forward stage, the 
gas which did not go forward, must be sent back to one of 
the previous stages. It cannot be discarded as it contains 
a greater proportion of U935 than the original gas to the 
first separation stage. This means that the quantities of 
gas being, handled decrease as we go along the process to 
the final stage, so that for only a small output from the 
unit, there will be huge gas volumes to handle in the early 
stages. Thus large compressors will be required for the 
early stages, and large areas of porous membrane or bar- 
rier material. The volume of gas circulating throughout 
the' system at any time is about 100,000 times the output 
from the final stage. 
Obtaining suitable barrier material was one of the 
biggest problems. In order for the barrier to work effi- 
ciently the diameter of the holes in it must be no more 
than one tenth that of the free path of the molecule. We 
have previously said that the free path is about 10"5 cm. 
Thus the holes must be 10“6 cm. or four ten millionths of 
an inch in diameter. Furthermore, these holes must not 
be plugged by dust particles in the gas stream, or by cor- 
rosive effects of the gas. Since the diameter, and there- 
fore the area of the holes, -is so small, a great number of 
them per unit area is required to get any throughput in the 
unit, without using exceedingly high pressures to force the 
gas through. The actual pressures used in the plant cor- 
respond to about one atmosphere differential between the 
two sides of the barrier, and the barrier must have suf- 
ficient mechanical strength to withstand this pressure dif- 
ferential. 
Another great difficulty in operation of this plant, which 
is one used for production oi U235 at Oak Ridge, is the need 
for supplying adequate protection to personnel against the 
harmful radiations from the radioactive decay of both U235 
and U238* Of the Two, the U235 has the shorter half-life, 
about half billion years, compared to about five billion years 
for U233. Thus it gives more radiation for a given weight in 
a given time. However, the U238 is present in much larger 
quantities, so that the, two isotopes are about equally danger- 
ous physiologically. The fact that there are large quantities 
of the radioactive materials present means that a great num- 
ber of very penetrating beta and gamma rays are continually 
being given out; therefore thick concrete walls are necessary 
to shield the operating personnel. Actually, the amount of 
operating personnel in the plant is very small, since the plant 
is operated almost completely by automatically controlled 
instruments 
1'he entire plant is shaped like a large U, with mat- 
erials flowing into the plant at one end of the U, and out 
of the plant at the other. This large U is composed of 
qq 
v-* v> smaller ones through which the material flows in similar 
manner to the flow in the main U. Although the structure 
consists of six floors, there are no personnel on any 
floor but the top, and here their main job is only to make 
the rounds and read the instruments assembled along the 
walls of this floor. The actual operation of the plant is 
controlled by a small group of men in a master control 
room outside the main plant. The number of instruments 
for the recording and controlling of temperatures, press- 
ures, flow rates, and so on in this plant is very large. 
According to a well known authority, this number exceeds 
the number put into all other new industrial plants in the 
country during the war. 
C. Thermal Diffusion Methods 
The principle of separation by thermal diffusion is 
not easy to understand. When a mixture of isotopes, in 
either a liquid or gaseous state, is placed in a chamber 
having cold walls with a hot tube or wire down its center, 
there is a tendency for the lighter molecules to diffuse to 
the interior, and the heavier ones to the exterior. Consid- 
erable work was done in the study of separation by 
thermal diffusion in liquids by Drs. Gunn and Abelson and 
their co-workers at the Naval Research Laboratory. 
Other groups investigated separation in gases by thermal 
diffusion. These processes were found to be possible ones 
for the separation of isotopes of uranium, but were not as 
practical as the gaseous diffusion method, and were not 
put into large scale production. 
D. Electromagnetic Methods of 
Separation 
The principle of the electromagnetic methods of sep- 
aration of the isotopes is the same as that of the Mass 
Spectrograph previously described. This work was mainly 
carried on by A.O. .Nier, at the University of Minnesota, 
and by E.O. Lawrence at the University of California. The 
chief difficulties of the electromagnetic method are (1) the 
difficulty of producing positively charged ions in the desired 
quantities; (2) the limited fraction of these ions used; and 
(3) effect of space charge. Only a small fraction of the 
ions produced are used, since the slits added to the mach- 
ine to narrow the beam, cause those ions outside the slit 
openings to be rejected. Space charge effects enter if we 
try to use too concentrated an ion beam. Then the in- 
dividual ions repel one another because of their like char- 
ges and tend to spread out the beam. In order to attain 
efficient separation, a thin, well focussed beam is nec- 
essary. This need not be as sharp as the beam used by 
Aston and Nier for the determination of exact atomic 
eo weights, and relative isotope abundance; nevertheless, 
focussing must be sufficient to obtain a relatively pure 
product. 
The first experimental work with the mass spectro- 
graph for the separation of the uranium isotopes was done 
by Nier and his co-workers, who were able to obtain only 
one microgram of pure U935, per sixteen hour day. This 
was, of course, too small an amount to be practical for 
making an atomic bomb, but the quantities obtained by Nier 
were used in early research work on the properties of 
1123(5, and showed that it was the isotope which was readily 
fissionable. In order to make larger quantities of the pure 
U23R for further investigations, Lawrence et. al. perfected 
the '“Calutron.” This machine utilized the giant magnet 
which had originally been intended for the giant cyclotron 
at Berkeley, Cal. This magnet has pole pieces 184 inches 
in diameter, and the air gap between poles is 72 inches. 
The Calutron solved the three difficulties mentioned in the 
preceeding paragraph. The third difficulty, that of space 
charge effects, was largely eliminated by the ionization of 
the residual gas in the chamber through which the ionic 
beams travelled. This large quantitiy of positive ions in 
the chamber tends to prevent the ions in the beam spread- 
ing out from one another and broadening the beam. The 
details of this improvement, as well as the methods by 
which the other two difficulties were solved, have not been 
made public. In the “Smyth Report on Atomic Energy” it 
is mentioned that the capacity of the Calutron was increas- 
ed considerably by having more than one beam at a time 
in operation in the magnetic field; but again the method of 
doing this is not described. 
It is known that several Calutrons were set up and 
operated, but their capacity was probably not more than a 
few grams of pure U235 Per day. Apparently the main 
value of the Calutrons was in the production of small 
quantities of pure U935 for investigation and research, 
while the mass production was accomplished by means of 
gaseous diffusion plant. Several other magnetic separation 
methods were investigated - the Isotron, Magnetron, and 
Ionic Centifuge. Little has been revealed about them, but 
it is probable that they were not found as practicable as 
the Calutron, although the isotron, at least, was proved 
workable. These methods are only mention in passing so 
that the reader will recognize the terms if he again hears 
of them. 
Summary of the Uranium Production Problem 
In this section we have shown that the discovery of 
the fission of uranium by neutrons, and the simultaneous 
780393 0—48 5 
61 liberation of great quantities of energy spurred nuclear 
physicists to seek a self-sustaining reaction which would 
liberate this energy in large quantities. Separation of the 
isotopes of uranium from natural sources showed that the 
active material in the fission was not the more abundant 
U238 but the less abundant U235. 0I*der for the reac- 
tion to be self-sustaining by means of a branching chain 
reaction it is necessary to have either pure U235, or at 
least material containing a much higher percentage of it 
than do natural sources. Thus methods had to be worked 
out for the separation of the isotopes. Because chemical 
means are not effective, physical methods, depending on 
only slight differences in mass or molecular velocity must 
be employed. Centrifuging and thermal diffusion methods 
in liquids and gases .were not found practical for large 
scale operation. After the solution of many unusual and 
difficult production problems, gaseous diffusion through 
porous membranes was found to be the best method for 
large scale production. 
Electromagnetic methods including the Calutron, Iso- 
tron, and Ionic Centrifuge were satisfactory for the pro- 
duction of small quantities of very pure materials, and 
were used mainly for research and investigation purposes. 
Of theses only the Calutron showed real promise, and the 
thermal 
DIFFUSION METHOD 
2 GASEOUS DIFFUSION 
THROUGH BARRIERS 
2 CENTRIFUGAL 
Fund uranium circulates, 
TENDS TV CONCENTRATE 
Lighter uzss at top 
Lighter u235 gas passes 
MORE READILY THROUGH 
BARRIER. 
WHEN MIXTURE OF GASIFIED U23S 
AMP 0238 /S SPUN RAP!PLY. 
LIGHTER 0238 FENDS TOWARD CENTER 
Fig. 33 Three Methods for Separation of Uranium Isotopes. 
62 others were abandoned. Calutrons operate on the same 
principle as the mass spectrograph, but have a much 
greater output because of larger units used, which permit 
the use of stronger magnetic fields. 
b3 SLOW NEUTRON 
REACTIONS 
PLUTONIUM PRODUCTION. THE HANFORD PLANT 
In a previous section we discussed the possibilities of 
obtaining a neutron branching chain reaction with various ele- 
ments at the heavy end of the periodic table. We saw 
that only with U235 is such a reaction possible, and then 
only when the U235 is in a much purer form than in nature, 
where each atom of U235 associated with about 140 
atoms of U238* As we previously said, the harmful effect 
which the 1X233 as on the maintenance of the reaction is 
that it captures the neutrons without emitting more of them, 
and thus the number of neutrons decreases rather than in- 
creases. We also learned that not all of the neutrons 
which the U235 itself, captures are successful in produc- 
ing fission. Many of the nuclei re-emit the neutrcns in a 
much less energetic state than that in which they entered 
the nuclei, and such “weak” neutrons do not aid the chain 
reaction. There is a third factor which must be consider- 
ed: the loss of neutrons at the surface of the reacting 
material. Since the neutrons are moving about in the bulk 
of the material haphazardly in all directions, and since, as 
we know, most of the volume of any mass of material is 
merely space, many neutrons will escape through this emp- 
ty space from the reacting mass, and thus will be lost. 
Therefore we see that the only process in the react- 
ing mass which produces neutrons to maintain the chain re- 
action is fission of U235, but there are three processes 
which are using up neutrons and tending to cause their 
number to decrease: non-fission capture of neutrons by 1X935, 
non-fission capture by U238, and escape of neutrons through 
the surface of the reacting material. Since U235 is more 
readily fissionable than U238> we may neglect the number of 
neutrons produced by the U238 fission. We must also consid- 
er non-fission capture of neutrons by other materials, which 
are imputities in our reacting mass. What can we do to in- 
crease the probability of obtaining the desired chain reaction 
by eliminating or lessening the factors which cause, 
the losses? 
G4 To minimize the effect of impurities all we need do 
is get rid of the impurities. This is easier said than done, 
since some impurities have very noticeable effects even at 
concentrations as low as several parts per million, and it 
is difficult to produce large quantities of materials of such 
purity. The diluting effect of the U238 can be remedied 
only by getting rid of the U238, but as we saw in the last 
section, the separation of the two isotopes is very difficult. 
Fig. 34 Fission of Uranium Caused by Neutron Adsorption. 
(a) Neutron approaches uranium nucleus, (b) Neutron captured by nucleus, (c) Excited 
nucleus vibrates due to energy excess, (d) Excited nucleus begins fission, (e) Two fission 
fragments are repelled with a large amount of kinetic energy. 
Fig. 35 Neutron Absorption by Uranium Without Fission Production. 
(a) Neutron approaching uranium nucleus, (b) Neutron penetrates nucleus, (c) Nucleus 
•n "Excited" state, emits gamma rays, and (d) dissipates excess energy, stabilizing to- 
la) heavier, unexcited nucleus. 
Critical Size 
The escape of neutrons through the surface of the re- 
acting mass is one effect we should be able to remedy. If 
we increase the size of the reacting mass, retaining the 
same shape, say that of a cube or sphere, we know that 
the volume of the material increases as the cube of any 
characteristic demension, L, while the surface increases 
only as the square, lA Since the total amount of mater- 
ial, and the number of nuclei undergoing fission is propor- 
tional to the volume, L3, while the number of neutrons es- 
caping through the surface is proportional only to the sur- 
face Ij2, the net effect of increasing the size of the reac- 
ting mass is to increase the possibility of maintaing the 
self-sustaining chain reaction, as the cube of any number 
greater than one increases more rapidly than its square. 
In other words, when we use a larger reacting mass, we 
cause more peutrons to be created by fission of U235 than 
are lost by escape through the surface of the material. 
Suppose we take a given quantity of uranium of a certain 
purity and a certain ratio of U238: Now, by adding 
more material to the original, but retaining the same shape, 
let us increase the size of the material on hand. We will 
85 eventually reach a size for which the number of neutrons 
being produced by the fission of U235 is just balanced by 
the number lost to the U938, to non-fission of U235, to im- 
purities, and by escape through the surface. For mis 
size the number of neutrons will remain constant through 
the mass. Increasing the size an infinitesimal amount more 
causes the number to increase rapidly. The reaction is 
now self-sustaining. The size at which this occurs is 
known as the critical size. A little thought will show that 
the critical size can be decreased (1) by decreasing the 
amount of impurities, i.e., using highly purified uranium, 
(2) by ridding the U235 of U238 by separating the two iso- 
topes (if the isotopes are only partially separated, the 
greater the U235 content of the mixture, the smaller the 
critical size), and (3) by using the shape of reacting mass 
which has the smallest surface to volume ratio (that is, 
a sphere). 
Even if pure U235 is used, there will still be a 
critical size for the chain reaction to occur. This is be- 
cause of the long “free path” 
of the neutron. As was ex- 
plained in an early section , 
the free path of a gaseous 
molecule is the distance it 
travels, on the average, be- 
fore colliding with another 
gaseous molecule. At atmo- 
spheric temperatures and 
pressures the free path is 
about 10" 5 cm. The free 
path of the neutron is the dis- 
tance it must travel from one 
nucleus before shrinking an- 
other nucleus. If we consider 
the nuclei as stationary, by 
knowing (1) the target area of 
a nucleus, which is just its 
projection perpendicular to 
the path of the neutron, and 
(2) the total number atoms in 
a plane, we can calculate the 
total area in a particular plane 
of atoms. The number of atoms 
in a plane can be calculated 
from the nuclear diameter 
and density of the material. 
The total area of the nuclei in 
Fig. 36 Determination of Cri- 
tical Size of a Uranium-Car- 
bon Pile. 
n r' 
DO the plane, divided by the total area of the plane, gives the 
probability of the neutron's hitting a nucleus in that plane. 
From a knowledge of the material's density and nuclear 
diameter, we can calculate the number of planes or layers 
cm* the .material perpendicular to the 
neutron s path. The reciprocal of the probability of hit- 
one plane gives the number of planes 
through which the neutron must go to be assured of a hit 
and this number divided by the number of planes or layers 
number of cm. through which it must 
traY?1* Thls V3, free oath through the material. 
The value of the free path 
of the neutron is of the order 
of 10 cm., which means that 
the neutron must travel ten 
cm. on the average before 
hitting another nucleus. 
Thus, if the reacting mass 
were spherical, it would have 
a critical size of 10 cm. ra- 
dius. The exact calculation 
of the free path is complica- 
ted because the neutron’s 
collision with a nucleus 
causes two more neutrons to 
be emitted, rather than only 
one; however, the order of 
magnitude is correct. Cri- 
tical sizes also exist for all chemical reactions, but be- 
cause of the small free paths for chemical reactions, the 
critical sizes are very small, and usually does not have to 
be considered. 
The target area, discussed in a previous paragraph, 
gives a direct measure of the probability of the neutron's 
hitting the nucleus, if there are no other forces which need 
be considered. However, if the nucleus repels the neutron 
or other bombarding particle, (e.g., a proton) the bombard- 
ing particles will have a smaller chance of reaching the 
hucleus. Thus, the repulsion has the same effect as re- 
ducing the target area, or as the nuclear physicist call it, 
the “ 'cross section. " Conversely, an attraction of the 
nucleus for the bombarding particles has the same effect 
as enlarging the cross section. Thus, the cross section or 
target area is seen to depend not only on the actual size 
of the nucleus being bombarded, but also upon other fac- 
tors, the most important of which are the nature of the 
bombarding particles, and their speeds. 
Fig. 37 Free Path of Neutrons 
in Natter. 
In the preceding paragraphs, we did not discuss the 
means of reducing non-fission capture of neutrons by U235. 
67 There is really little that we can do about this. The num- 
ber of neutrons causing fission and the number being re- 
emitted are equal to the numbers having energies in ex- 
cess of the activational energies for fission and re-emis- 
sion respectively. These numbers depend only on the 
activational energies for the two processes and on the tem- 
perature. The temperature has very little effect until we 
reach extremely high temperatures, which are beyond the 
realm of practicality, so that we may assume that the re- 
lative numbers of nuclei undergoing the two processes do 
not change. 
Slow Neutron Reactions 
We now come to a very interesting and important 
point. In all of our previous discussions we have been 
considering the fast neutrons emitted by the fissioning 
atoms. These fast neutrons have energies of the order of 
one to two Mev, and velocities of about l/20th that of 
light. However, it was found by researchers of the Man- 
hattan District that slow neutrons are also very effective 
in producing fission of U235. The slow neutron reaction of 
a resonance process, and occurs when the neutron 
has an energy of about 1/40 ev. At this energy level the 
neutrons are moving with greatly reduced velocities. In 
fact their average velocity is about that of hydrogen mole- 
cules at the same temperature, and is around ten thousand 
times slower than that of the fast neutrons of several Mev 
energy content. Since the only motion and energy which 
these neutrons possess is that due to the thermal motion 
of gases according to the kinetic theory, they are often 
called “slow or thermal” neutrons. The effectiveness of 
a slow neutron depends on the fact that it has an'energy 
corresponding to that of a certain resonance level in the 
uranium nucleus, and thus is able to leak through the poten- 
tialenergy barrier, even though it can not get over it, pen- 
etrate the nucleus, and cause its rupture or fission. 
The discovery of the resonance capture of slow neut- 
rons by U935 offers a method of increasing the possibili- 
ties of maintaining the chain reaction. When we discussed 
the possibility of maintaining a chain reaction by increas- 
ing the size of the reacting mass to the critical size, we 
saw that the critical size decreases as the ratio of the 
U23r to U230 increases. Actually, using a natural uranium 
source in which this ratio is only about 1:140, it is impos- 
sible to maintain a chain reaction, no matter how large the 
mass is made. If the mass is made extremely large, so 
that only a negligible number of neutrons are escaping 
through the surface, the chain reaction will still not occur, 
as too many neutrons are being captured by the U233. 
H we slow down the neutrons so that their energy is at the 
68 normal level (1/40 ev), they will not have sufficient act- 
ive tional energy to pass the barrier of U238. It has been 
found that neutrons can be slowed by elastic collision with 
the atoms of certain substances notable graphite, to the 
thermal level. At this level, then, fission of U235 becomes 
the most probable reaction. 
There is a slight drawback here, however. The U238 
also has resonant, levels at which it captures neutrons, with- 
out causing fission. An important resonance level occurs 
for neutrons having an energy of about 25 ev. Therefore, 
the -neutrons will have to be kept out of the neighborhood of 
U238 while, they have energies of 2b ev, and until their energy 
has been reduced to l/40th ev. The maintenance of the chain 
reaction by the principles we have just discussed is effected 
by means of the so-called “uranium pile.” Briefly, the pile 
consists of small chunks of uranium or uranium compound, 
interspersed in a particular form (exact nature secret) or lat- 
tice between other chunks of material used to slow down the 
neutrons. The material which slows the neutrons is known as 
a moderator since it “moderates” the neutrons’ speed and re- 
flects them back to other chunks of uranium when they can re- 
act. 
Let us recapitulate a little on the operation of the 
pile. A source of neutrons, .produced for example from a 
small quantity of radium and beryllium, is placed within the 
pile. Let us consider only one of these neutrons. We may 
assume that it is able to cause the fission of one uranium 
nucleus since it has high enough speed to overcome the fis- 
sion activation energy. The fission produceds two more 
neutrons, elements of lower at. wt. than U, and 200 Mev of 
energy. This energy will be the kinetic energy of such 
atoms as those of krypton from U23R disintegration; the 
two atoms produced by the fission will be moving apart 
with great speed, and will collide with other atoms in the 
pile, until all of their kinetic energy is dissipated as heat. 
If the volume of the moderator material is much greater 
than that of the little chunks of uranium, and the chunks 
are of smaller size than the free path of the neutron, the 
two neutrons will be ejected into the moderator. There 
they will collide with the material composing the modera- 
tor and will be slowed down by bouncing around in it un- 
til they find‘their way back into the uranium chunks. 
Suppose only one of these neutrons causes fission of U 
235, while the other is caught by U238 or some impurity and 
thus is lost to the U235. A neutron which is caught by U235 
but does not cause fission will be slowed down greatly, and 
can be further slowed down by collision with other moderator 
69 atoms. Hence it will not be lost unless it is captured by the 
U238 or escapes through the surface of the pile. With one 
neutron producing only one more effective neutron for fission, 
the pile is self-sustaining and stable. Increasing the size of 
the pile will minimize the number of neutrons escaping from 
its surface; use of very pure materials in the moderator will 
minimize the neutron capture by impurities, and non-fis- 
sion capture by U235 may be neglected insofar as it 
causes reduction of neutrons. Thus we can regulate our 
conditions, so that of each two neutrons being produced by 
a fissioning atom, one will produce further fission in U235, 
and the other, will be captured by the U238. 
The first successful experiments were performed with 
the pile at the University of Chicago early in 1942. The 
pile was built of successive layers of moderator (graphite) 
and uranium, until the critical size was reached. It was 
then operated at such a rate that the energy given off by 
the disintegrating U235 atoms was at a rate equivalent to 
an electrical power production of one-half watt. Later, 
the rate was stepped up to 200 watts. A very important 
point must be now mentioned - the method of controlling 
the pile. 
Once the pile reaches critical size, the number of 
neutrons in action at a given time will build up very rapid- 
ly according to an exponential law, and, if uncontrolled, 
will result in an explosion. Suppose that the pile is of 
such construction that each neutron formed gives on the 
average 1.05 more neutrons which are effective in produc- 
ing farther fission. Then after two steps there will be 
(1.05)2 neutrons available, after one hundred steps, (1.05)100, 
etc. The value of (1.05)luois about 100, so that after a 
hundred steps, there will be one hundred available neutrons, 
after two hundred steps, - 100 x 100 = 10,000, and after 
three hundred steps a million neutrons, for each original 
neutron sent into the pile. The time for each step in the 
reaction is only about a millionth of a second, so that if 
no adequate controls were provided, within a time much 
shorter than a second, the whole pile could react and 
cause a violent explosion, once the critical size was reach- 
ed or slightly exceeded. 
The control of the reaction is very simple: it mere- 
ly consists of inserting a controlled amound of “impurities” 
into the pile. This is done by providing channels in the 
pile mass through which rods of cadmium or boron steel 
may be inserted. These materials have a very high affin- 
ity for slow neutrons, and capture them, thus slowing down 
the reaction. If it is necessary to slow the reaction only 
slightly, the rods are pushed in only a short distance; con- 
versely, to effect a considerable reduction the rods may be 
70 Fig. 38 Action of Uranium-Carbon Pile. 
The initiating neutron from an outside source works its way through the carbon atoms, 
striking an uranium nucleus at A, and causing its fission. Two more neutrons are emitted by 
the disintegrating nucleus. The neutron following path (I) collides with carbon nuclei', these 
collisions reducing its speed until it is able to cause the disintegration of another uranium 
nucleus at B. This disintegrating nucleus gives two more neutrons. The neutron following 
path (3) passes through the uranium mass C without causing disintegration, and proceeds 
to D, where it causes further reaction. The neutron proceeding along path (2) is captured 
by the uranium nucleus at E, since it is moving at a relatively high speed. The neutron 
following path (4) escapes through the surface of the pile. The distance between collisions 
is proportional to the velocity of the moving neutron. 
pushed in farther, or the reaction may be brought to a 
stand-still if desired. 
Delayed .Neutrons 
As we just stated, the time between successive steps 
in the reaction is very small, and once the multiplication 
factor only slightly exceeds 1.000, we would expect the re- 
action rate to increase in such a short time that an opera- 
tor would not be able to adjust the controls quickly enough 
to prevent the reaction’s getting out of hand. 
This is what would happen were it not for the fortun- 
ate phenomena occurring in the pile, and resulting in the 
production of “delayed neutrons. ’ It has been found that 
not all of the neutrons resulting from the Uggc fission are 
emitted instantaneously, that is within a few millionths of 
a second, but one per cent are delayed at least 0.01 sec- 
ond, and about 0.1 per cent are delayed as long as a min- 
ute. Thus with automatic recording and regulating instru- 
ments, there is time to regulate the controls to the de- 
71 sired values of neutron intensity in the pile. For example 
we might operate a pile of such a size so that without in- 
sertion of control rods its multiplication factor is only 
1.001. Thus every thousand neutrons produced in any given 
step will cause the appearance of 990 more within 0.01 
second, 1000 within a minute, and 1001 in a slightly longer 
time than a minute. It is only the last one neutron of the 
thousand and one which causes the reaction rate to increa- 
se, and we can easily control this last neutron with the 
control rods. 
Let us investigate the cause of slow neutron emission. 
When the U235 disintegrates, we know that it gives several 
free neutrons as well as two fragments of nearly equal 
size (that is, of about one-half the atomic number and at- 
omic weight of uranium). Consider these two large nuclear 
fragments. The original U235 contained 92 protons and 
143 neutrons, and its n/p ratio was about 1.6. If three 
of the neutrons are given off by the fission, each, remain- 
ing half of the nucleus will then contain 143 — 3 . 70 
2 
neutrons, and 92/2 * 46 protons, and its n/p ratio will 
also be about l.o. However, an element of atomic number 
46 is in the middle of the periodic table, and in the third 
chapter we learned that the stable n/p ratio for elements 
in the middle of the table is about 1.3. Thus, the frag- 
ments given off by the U235 fission are not stable and tend 
to stabilize themselves to elements having permissable ra- 
tions. The n/p ratio is too large; however, it may be de- 
creased either by increasing the number of protons or de- 
creasing the number of neutrons. Actually, the unstable 
fission fragments do both. They convert some of the. neu- 
trons into protons by emitting electrons or beta rays. We 
recall that a neutron may be considered a combination of 
a proton and an electron. The emission of beta rays fol- 
lows the usual laws of radioactive decay, and accounts for 
much of the danger to personnel caused by atomic bomb 
residues as well as by the materials in the uranium pile. 
Since the activational energy for beta ray emission is less 
than that for emission of the large, heavy neutrons from 
the nucleus, beta ray emission is favored over neutron 
emission. However, there are still a few of the unstable 
fragments which have enough energy to liberate neutrons. 
This is not an instantaneous process, but a rather slow on$ 
and it accounts for the production of the delayed neutrons 
which are so useful in controlling the pile. 
Moderators 
It is necessary that we consider in a little more de- 
tail the problems which the Manhattan District solved in ob- 
taining a suitable moderator. There are two main require- 
72 ments which the moderator must fulfill. First, it must 
slow down the neutrons sufficiently as desired, and second, 
it must not, itself, capture the neutrons and thus make 
them unavailable for production of further fission. In ad- 
dition to these requirements, it must be possible to obtain 
the moderator material in the desired quantities, and the 
material must have the correct structural properties for 
use in the pile. 
The neutrons are slowed down by collisions with atoms 
of the moderator, during which collisions they give up a 
portion of their kinetic energy to the atoms with which they 
collide. The most effective atoms for slowing the neutrons 
are those having weights closest to that of the neutron. 
The hydrogen atom has nearly the same weight as the neu- 
tron, and a collision between a neutron and a hydrogen at- 
om moving only at thermal velocities results in the neut- 
ron's losing about 40% of its energy, on the average. It 
can be easily shown that in about thirty-five collisions, the 
neutron's energy will be reduced from 2 Mev to 1/40 ev. 
Because compounds of hydrogen will be equally effective, 
water and other hydrogenous materials, such as paraffin, 
are often used as shields against fast neutrons. However, 
hydrogen does not satisfy our second requirement, that it 
must not capture the neutrons; in fact, it very readily 
combines with neutrons to form heavy hydrogen, or deu- 
terium. i 1 9 
iH1 + oH1 = ]H2 
The facility with which hydrogen combines with neutrons is 
one of the reasons for the very harmful effect of neutrons 
on the human body, because the body is composed mainly 
of hydrogenous materials. 
The lightest atom after hydrogen is heavy hydrogen 
or deuterium, having an atomic weight of two. It would be 
satisfactory as a moderator, and, in fact, some piles were 
operated using deuterium as a moderator. The deuterium 
was in the form of heavy water, and remained a liquid in the 
pile. This is somewhat a disadvantage to pile construc- 
tion, but the heavy hydrogen could be converted into solid 
compounds, which might possibly be of more utility. The 
drawback to deuterium use is the lack of sufficient quanti- 
ties of it in a pure state. Although deuterium is found in 
all natural sources containing hydrogen, it occurs as only 
0.02% of the total hydrogen. The separation Of deuterium 
from hydrogen presents us with the usual difficulties of 
isotope separation with which we were familiarized in the 
previous section. However, the isotope separation is eas- 
ier than for those of U because of the much larger ratio 
of masses for the two hydrogen isotopes, 2:1, as compared 
to 1.009:1 for the uranium isotopes. Cf the many methods 
73 which have been used for the preparation of heavy hydro- 
gen or its compounds, the most common commercial one 
is the electrolysis of water. If only a portion of a given 
quantity of water is electrolyzed, then by a process of fra- 
ctional electrolysis the proportion of deuterium in the hy- 
drogen source may be considerably increased. This pro- 
cess depends on a cheap source of electric power, and for 
this reason the Germans erected units for production of 
heavy water in Norway. Dr. Niels Bohr, propounder of the 
Bohr theory, was forced by the Germans to work on this 
project before his abduction to the United States by com- 
mando units, who later destroyed the plant. 
After deuterium, the light- 
est atoms are those of He, Li, 
Be, B, and C. Helium is not 
practical as a moderator be- 
cause it is a gas and forms no 
compounds. Lithium and boron 
both capture slow neutrons, 
and thus cannot be used satis- 
factorily as moderators. Ber- 
yllium is not an abundant ele- 
ment, and cannot be obtained 
in sufficient amounts of the 
required purity. This leaves 
carbon, which, after methods 
had been devised for prepar- 
ing it in a very pure state, 
was the actual material used 
as a moderator. 
Power Output From Pile 
As we have learned, the 
pile operates by a continuous 
chain reaction which causes 
the disintegration of U235 to 
lighter, radioactive elements, 
and results in the production 
of 200 Mev of kinetic energy 
in the disintegration products. 
This energy is converted into heat, and the ability to carry 
away the heat of the reaction controls the speed at which 
the pile can be allowed to operate. For a pile operating 
only at a low power level, the heat may be dissipiated to 
the surroundings by radiation and convection, etc. However, 
for a large unit, or one operating at a higher power level, 
other, swifter means of removing the heat of reaction must 
Fig. 39 Scheme of the Uranium 
Carbon Pile and Controls. 
74 be employed. This can be done by means of pipes contain- 
ing circulating water or other heat transfer media. The 
utilization of the heat of reaction from the iple is the basis 
of many of the proposed industrial, peacetime uses of 
atomic energy. 
Plutonium - The Hanford Project 
Throughout this section, we have talked about the non- 
fission1 capture of neutrons by U238- The inquisitive 
reader will naturally ask, “What are the results of the re- 
action between the neutron and U238?” It has been found 
that this reaction is merely a simple capture, resulting in 
the formation of a heavier isotope of uranium, U239. This 
isotope is unstable, and by radioactive decay and emission 
of an electron is transformed into a new element-Neptunium, 
g„Np^9. The Neptunium is also unstable, and by a similar 
radioactive decay process it is transformed into another 
new element Plutonium, 239. This new element, Pu, 
is fairly stable as far as radioactive decay is concerned, 
but is similar to U235 in its instability to neutron attack. 
However, since it has an atomic number different from that 
of uranium, it is a different element, with different chemi- 
cal properties, and can be separated from U238 by chemi- 
cal means. These chemical means are much less dif- 
ficult than the isotope separation methods we have consid- 
ered. We may summarize the reactions as follows: 
(1) + = 9gU239 
(2) 92U239 = 93Np239 + _ieo, half-life 
°f 92U339 — 20 min. 
(3) 93Np239 - 239 —ie°> half-life 
of gsNp — 2 days 
(4) 94Pu239 = 92U235 + 2He4, half-life 
of 94Pu239>— 25,000 yrs. 
Thus we see that the pile is continuously producing 
Pu as wen as Np and U239. If we consider that each fis- 
sioning IJ235 atom gives two neutrons, but only one is used 
to maintain the chain reaction, the other one, as we pre- 
viously learned, is being lost to U238> to impurities, and 
through surface escape. If we use very pure materials, 
and a very large ratio of volume to surface, for practical 
purposes the other neutron may be considered as being 
lost to the U238 alone. Since each neutron captured by an 
atom of U238 results eventually in the production of an 
atom of Pu. we will have one atom of Pu formed for each 
75 atom of U235 reacted. Thus, a uranium source containing 
0.7% U935 could be converted into a material containing 
0.7% Pu, if all of the U235 were used. 
The chemical and physical properties of Pu were 
studied, even before large quantities of it were produced, 
and a suitable chemical method was worked out for sep- 
arating the small amount of Pu from the Ugsg and fission 
products of the U935. Security regulations permit very 
little to be said about this process. Suffice it to say that 
by the usual chemical means of precipitation, solution, re- 
precipitation, etc. the Pu can be successfully separated, 
and prepared in the desired state of purity. The Pu has 
two important chemical oxidation states 
and the chemical processes usually make use of alter- 
nations between these two states. 
The successful separation of Pu from the other mat- 
erials in the pile, and its ability to undergo fission in a 
manner similar to that of and thus be used in place 
of U235 for the fissionable material of the atomic bomb, 
led to the construction of the large uranium piles near 
Pasco, Washington. This is the Hanford Project. The 
plant is located on the Columbia River, which provides a 
large supply of the fresh water needed for chemical pro- 
cessing as well as for carrying away the heat generated by 
the reactions in the pile. The magnitude of the heat gen- 
erated may be realized, when it is considered that the 
cooling water, which is returned to the river after passing 
through the piles, causes an appreciable temperature rise 
throughout the whole Columbia River just below the plant 
site. 
There are many practical difficulties, chemical, 
physical, biological, and engineering, which had to be sol- 
ved at this plant. All operations must be carried on by 
remote control, with the operators protected from the rad- 
ioactive materials by heavy concrete walls. The pile con- 
tains uranium in “cans” made of a material which is able 
to withstand the action of the radiations, the corrosive 
effect of cooling water, btc., but which does not capture 
too many neutrons itself. It is believed that cooling water 
runs over the surface of the cans. The reaction is not 
continued until all of the U935 is consumed. This would 
require too long a time to be practical. When the cans 
have been in the pile a sufficient length of time, they are 
automatically pushed out, and fresh cans of U235 and U238 
replace the partially spent ones. The cans and their con- 
tents are then dissolved in acid, and the chemical separa- 
tion processes started. The materials in the separation 
plant flow in continuous streams, all flows being remotely 
76 controlled. The plant resembles a series of small “can- 
yons as the open spaces between concrete walls of the 
different units are called. 
The main danger to personnel is the presence of the 
radioactive fission products of the U235. The water dum- 
ped back into the river must not be contaminated by these 
products and the fact that some of the radioactive mater- 
ials are gasses necessitates that numberous steps be taken 
to assure that they do not foul the surrounding atmosphere 
Very rigid precautions were taken at this plant, as well as 
at the Clinton plant and in other units and laboratories 
where radioactive materials were handled. 
7M03«a ()—4H 6 
77 THE ATOMIC BOMB AT 
HIROSHIMA 
EXPLOSION: THEORY AND PRACTICE 
In the previous sections we have discussed atomic and 
nuclear theory in some detail so that the reader may be 
able to understand the development of the atomic bomb, and 
difficulties which beset its developers. In these sections 
we have been fortunate in being able to present a large 
quantitity of factual material. We now come to the section 
which will be climactic to most readers, and it is unfortun- 
ate that in this section we will be able to present very few 
facts, but only basic theory and conjecture as to the 
theory’s application. 
We have learned that a mass of U23R, Plutonium, or 
enriched Ugqg of size equal to or greater than critical, will 
detonate violently when exposed to a source of neutrons. 
However, no detonation can be effected in a mass of sub- 
critical size. The problem then resolves itself into the 
production of the or Pu in sufficient quantities of 
sufficient purity, and the bringing together of sub-critical 
masses of the explosive material in a satisfactory manner 
to form a critical or above critical mass, which wiH under 
go the chain reaction and detonate. 
We have already discussed the methods of producing 
the active material. This work was carried on by the 
Clinton and Hanford plants, by the Metallurgical Labora- 
tory, and by many other scientific institutions throughout 
the country. The second part of the problem, that of 
assembling the’ active material to form a bomb, was main- 
ly investigated by the Los Alamos Project, located in the 
arid regions of northern New Mexico, and headed by Dr. 
J.R. Oppenheimer. In this forbidding desert on July 16, 
1945 occurred the first man-made atomic explosion. The 
culmination of the concentrated effort of thousands of 
scientists, engineers, and workers, this explosion heralded 
the new age of atomic power. 
Before launching a discussion of the construction and 
operation of the atomic bomb, it will be useful for us to 
78 study first some of the basic concepts of explosions in 
general. An explosion is defined as the sudden generation 
and liberation of energy, occurring before the constituents 
which cause the reaction and the reaction products have 
had time to separate appreciably. 
The most important factor in determining whether or 
not an explosion occurs in a reacting mass is the speed of 
the reaction. If the energy of the reaction can be trans- 
ferred to the surroundings as rapidly as it is evolved, 
there is no explosion. On the other hand, an explosion is 
said to occur when the reaction products and energy can- 
not be dissipated as quickly as they are formed. There is 
no difference in the basic processes involved, only in the 
reaction rates. Thus a boiler producing steam does not 
normally cause an explosion, since the energy of the ex- 
panding steam is transferred to the machines which the 
steam operates. However, an explosion results when the 
steam cannot expand but is confined in the boiler. The 
pressure builds up until the walls of the boiler rupture. 
The sudden expansion of the gas (energy liberation) cannot 
be immediately absorbed by the boilers surroundings, 
and we say that an explosion has occurred. The same 
concepts hold for chemical reactions. Thus the burning of 
coal in air proceeds at a slow enough rate for the heat of 
the reaction to be dissipated. However, if the coal is fine- 
ly ground, heated, and thrown into a container of oxygen, 
the reaction proceeds so quickly that an explosion occurs. 
The so-called “high explosives” are usually chemi- 
cal compounds in the metastable state, such as TNT or 
nitroglycerin. By the addition of a small amount of activa- 
tion energy, as from a spark or shock, a reaction is in- 
itiated which generates quantities of gases in a time of 
approximately a micro second. In this short time, the re- 
action products cannot separate or expand as in normal 
reactions, and an explosion results. Pressures of the 
order of 10' lbs. per sq. in . occur during such explosions 
From what we have‘previously learned - that one pound of 
fissioning uranium produces energy equivalent to twenty 
miHion pounds of TNT - we should expect a much higher 
pressure to be produced by the atom bomb than by TNT. 
Presently we shall discuss the pressures encounted in the 
explosion of an atom bomb. 
Having obtained a clear idea of what we mean by an 
explosion, let us examine the relations between the various 
factors influencing an explosion. Our discussion wiH be 
only approximate, but it will give the general idea of the 
magnitudes of the factors considered. Let us assume a 
cube of explosive material such as TNT or uranium. Let 
the edge of the cube by L cm. and its density D. For 
79 simplicity we will suppose that the effect of the explosion 
is to fracture the cube into two equal fragments at a 
plane parallel to one of the faces of the cube. Suppose 
that the pressure generated and acting on these two newly 
formed faces has a uniform value P, and is generated in a 
time, T. The force on each inner face is the pressure 
times the area of the face. 
F = PL2 
(1) 
This force tends to drive the two faces apart, with an 
acceleration which we can easily calculate. Let the velo- 
city of separation of the two halves equal 2v, and the to- 
tal mass m. Then the total momentum is mv, and the 
force, which equals the rate of change of momentum, is 
_ mv 
F - 
(2) 
The total mass, m, is DL2. Substituting this value of m 
in equation (2), and equating the two expressions for the 
force in equations (1) and (2), we obtain 
2Pt = DLv. 
(3) 
If we assume further that during the time t the material 
expands to only twice its original volume, then the distance 
of expansion is L, and the velocity of expansion of each 
half of the original cube is v 
L 
V - t 
(4) 
Substituting this value of v into equation (3), and solving 
for t, we may obtain a expression 
t2 = 2P~ 
(5) 
Although this equation is based upon many assumptions 
which are rather approximate, It gives a very simple re- 
lations between the various factors, t, D,L, and P. Of 
particular importance is the relation between t and P. 
Notice that if D and L are held constant, t must decrease 
as P increases. 
If we substitute approximate values into the equation, 
using. TNT, let L equal one cm., D = 1 gm/cc., and P 
= 1012 dynes per cm2 (10' Ibs/sq.in.). This will give a 
value of t approximately equal to 10“° seconds or one 
micro second. Now using the same values of L and D, 
but remembering that the pressures developed by the atom 
bomb are roughly a million times greater than those by 
80 TNT, we can see that the time, t, will now be 
1 q 
— = 10“° times as great for the atomic bomb 
explosion. Hence, Hie atomic bomb reaction must take 
place in 10"° x 10“° * 10"9 seconds to cause the desired 
explosion. It is possible for the reaction to go completely 
in such a short time? 
We have previously said that the mean free path of a 
neutron in the uranium mass is about ten cm. If the neu- 
tron’s energy is one Mev, by substitution into the kinetic 
energy equation, 2 
K.E. = , we find that the neutron’s 
2 
velocity is about 109 cm. per second. Thus the time for 
the neutron to travel between two successive disintegrating 
10 8 
nuclei is or 10 sec. But this is the time for 
109 
only one step. For all the nuclei in one gram of uranium 
to be disintegrated, assuming for the moment that the chain 
reaction can be made to go in this small amount of mater- 
ial, we may calculate the number of steps needed. There,j 
are 6.03 X 235 = X 102-*- nuclei in a gram of 
uranium. Assuming that each step in the chain produces 
two neutrons, n steps will produce 2n neutrons. Equating 
2n - 2.5 X 1021 
(6) 
we can solve and find that n is about 71 steps. Since the 
actual bomb is larger than one gram, more steps will be 
required. We may use 100 steps as an approximation. 
the total reaction time will be about 100 X 10“° or 
10"° seconds. Therefore the reaction time for the atomic 
bomb is about the same as for a TNT bomb. 
This reaction time of 10"® is undesirable, as We just 
found that it should be only one-thousandth as great to 
assure complete reaction of the uranium. The difficulty 
lies in the fact that the reaction of the first fraction of 
the material drives the mass apart, so that a mass which 
was of critical size before the reaction began, soon con- 
sists of many sub-critical masses and the reaction rapidly 
comes to a halt. 
There are two things which can be done to alleviate 
this situation. One is the use of larger than critical 
masses of material. However, this change will not great- 
ly aid the reaction, as the number of critical masses 
must be held to practical limits of handling. The other 
improvement is to surround the active uranium mass by a 
heavy, inert, material, which will keep the fragments of 
81 the reacting material together for a short while. This 
material, called the ‘‘tamper/’ is made of a heavy metal 
such as lead. It has been found that the value of the tamper 
is practically independent of 
its mechanical strength, the 
most important property being 
its density. Materials of 
greatest density are most de- 
sirable for use as tampers. * 
The tamper also serves an- 
other purpose. This is the re- 
flection of stray neutrons, 
which might otherwise escape 
from the surface of the react- 
ing mass. Again, a dense mat- 
erial is desirable since it con- 
tains more nuclei per unit 
area, and has a better chance 
of reflecting the neutrons. This 
is analagous to thereflection 
of a golf ball from a thick for- 
est onto the fairway of the 
course. The denser the for- 
est, the mor probability there 
is that the ball will strike a 
tree and be reflected. Obvi- 
ously the tamper must be made 
of material which does not itself capture neutrons by any 
of the nuclear transmutation processes we have discussed. 
Despite the utilization of mqre than one critical mass 
for the bomb, supplemented by a tamper, it is well known 
that the bomb is rather inefficient. Hence, the measures 
are not too effective. It has been stated that the energy 
liberated by an atomic bomb is equivalent to that of 20,000 
tons of TNT. The energy liberated per pound of exploding 
TNT is approximately 5,000 btu per pound. Thus, the 
energy liberated by 20,000 tons of TNT may be calculated. 
This value is about the same as that theoretically obtainable 
by fission of only five pounds of U235. 
However, it it well known that the amount of mater- 
ial in the bomb is considerable greater than five pounds, 
probably several hundred pounds. Therefore, it can be de- 
duced that the bomb’s efficiency is rather low, probably 
only a few per cent. Further research will, no doubt, be 
directed toward methods of increasing the bomb’s efficiency. 
It has been stated that the bomb dropped on Nagasaki was 
CHARACTERISTIC LENGTH ~ tc/71 
DENS/T/= D 
F= PL2 
Fig. 40 Elementary Explosion 
Concepts* 
82 considerably more efficient or at least more effective than 
that dropped on Hiroshima. 
Assembly and Detonation of the Bomb 
The methods used to assemble and detonate the bomb 
are top military secrets, and only the roughest of conjec- 
tures may be presented here. If a mass of uranium of 
greater than critical size were made, it would detonate 
spontaneously, the reaction being instigated by stray neut- 
rons, which are always in the atmosphere as a result of 
cosmic ray activity. Hence, we -must start with two or 
more pieces of subcriticral size, and bring these pieces to- 
gether at the proper time in a short interval. This time 
interval must be small enough to insure that the parts of 
the bomb will not be blown apart by the reaction they ini- 
tiate before the reaction has been able to proceed to some 
extent. Because of the rapid reaction time (a micro sec- 
ond or less) we assume that the two parts must be 
brought together during a time interval no longer than a 
micro second. 
Let us assume that we have two pieces of less than 
critical size, their combined mass and shape being more 
than critical size. If these pieces are separated by an 
air gap 'of say one cm., there will be a sufficient number 
of neutrons escaping to prevent the chain reaction’s ensu- 
ing. If the distance separating the two halves of the bomb 
is one centimeter, and they must be brought together in a 
micro second or less, then ihe velocity of their approach 
must be no less than l/10“b or 10° cm. per second. This 
is a thousand meters per second, and is the same order 
of magnitude as the velocities of projectiles shot from 
military guns. This suggests that a projectile such as a 
slugh of k0 shot between the two halves forming a 
“weld” which will give, in effect, a solid mass of uran- 
ium above the critical size. Thus the chain reaction will 
be possible. 
Another method is shown 
schematically in figure 41 . 
However, it must be remem- 
bered that these methods are 
pure conjecture. We can only 
present enough material on 
the subject of the bomb con- 
struction and assembly, tam- 
pers, and critical mass to 
indicate theproblems which 
must be solved, and the gen- 
eral principles involved. 
Fig. 41 Schematic Representa- 
tions of Bomb Assembly, 
83 PERIODIC ARRANGEMENT OF THE ELEMENTS 
Series 
Period 
ZERO 
GROUP 
GROUP I 
r2o 
GROUP II 
RO 
GROUP III 
R2O3 
GROUP IV 
RHi RO2 
GROUP V 
RHs R2O5 
GROUP VI 
RH2 RO3 
GROUP VII 
RH RjOr 
GROUP VIII 
0 
1 
HYDROGEN 
H =1.0078 
No. 1 
2 
1 
HELIUM 
He. =4.002 
No. 2 
LITHIUM 
li =6.940 
No. 3 
BERYLLIUM 
Be. =9.02 
No. 4 
BORON 
B =10.82 
No. 5 
CARBON 
C =12.00 
No. 6 
NITROGEN 
N =14.008 
No. 7 
OXYGEN 
0=16.000 
No. 8 
FLUORINE 
F =19.00 
No. 9 
3 
2 
NEON 
Ne. =20.183 
No. 10 
SODIUM 
Na =22.997 
No. 11 
MAGNESIUM 
Mg. =24.32 
No. 12 
ALUMINUM 
A1 =26.97 
No. 13 
SILICON 
Si =28.06 
No. 14 
PHOSPHORUS 
P =31.02 
No. 15 
SULFUR 
S =32.06 
No. 16 
CHLORINE 
Cl =35.457 
No. 17 
4 
ARGON 
A. =39.944 
No. 18 
POTASSIUM 
K. =39.10 
No. 19 
CALCIUM 
Ca. =40.08 
No. 20 
SCANDIUM 
Sc. =45.10 
No. 21 
TITANIUM 
Ti =47.90 
No. 22 
VANADIUM 
V =50.95 
No. 23 
CHROMIUM 
Cr =52.01 
No. 24 
MANGANESE 
Mn =54.93 
No. 25 
IRON 
Fe =55.84 
No. 26 
COBALT 
' Co =58.94 
No. 27 
NICKEL 
Ni =68.69 
No. 28 
5 
COPPER 
Cu. =63.57 
No. 29 
ZINC 
Zn. =65.38 
No. 30 
GALLIUM 
Ga =69.72 
No. 31 
GERMANIUM 
Ge. =7260 
No. 32 
ARSENIC 
As =74.93 
No. 33 
SELENIUM 
Se =79.2 
No. 34 
BROMINE 
Br =79.916 
No. 35 
6 
KRYPTON 
Kr. =82.9 
No. 36 
RUBIDIUM 
Rb. =85.44 
No. 37 
STRONTIUM 
Sr. =87.63 
No. 38 
YTTRIUM 
Y =88.92 
No. 39 
ZIRCONIUM 
Zr. =91.22 
No. 40 
COLUMBIUM 
Cb =93.3 
No. 41 
MOLYBDENUM 
Mo. =96.0 
No. 42 
MASURIUM 
Ma=? 
No. 43 
RUTHENIUM 
Ru =101.7 
No. 44 
RHODIUM 
Rh =102.91 
No. 45 
PALLADIUM 
Pd =106.7 
No. 46 
7 
SILVER 
Ag. =107.880 
No. 47 
CADMIUM 
Cd. =112.41 
No. 48 
INDIUM 
In =114.8 
No. 49 
TIN 
Sn. =118.70 
No, 50 
ANTIMONY 
Sb =121.76 
No. 51 
TELLURIUM 
Te =127.5 
No. 52 
IODINE 
I =126.932 
No. 53 
8 
XENON 
Xe. =130.2 
No. 54 
CAESIUM 
Cs =132.81 
No. 55 
BARIUM 
Ba. =137.36 
No. 56 
LANTHANUM 
La =138.90 
No. 57 
CERIUM 
Ce =140.13 
No. 58 
9 
10 
6 
HAFNIUM 
Hf = 178.6 
No. 72 
TANTALUM 
Ta. =181.4 
No. 73 
TUNGSTEN 
W =184.0 
No. 74 
RHENIUM 
Ra. =186.31 
No. 75 
OSMIUM 
Os. =190.8 
No. 76 
IRIDIUM “ 
Ir. =193.1 
No. 77 
PLATINUM 
Pt. =195.23 
No. 78 
11 
GOLD 
Au =197.2 
No. 79 
MERCURY 
Hg =200.61 
No. 80 
THALLIUM 
T1 =204.39 
No. 81 
LEAD 
Pb =207.22 
No. 82 
BISMUTH 
Bi. =209.00 
No. 83 
POLONIUM 
Po. =209.99 
No. 84 
ALABAMINE 
Am. =? 
No. 85 
12 
7 
RADON 
Rn =222 
No. 86 
VtRGINIUM 
Va =? 
No. 87 
RADIUM 
Ra =225.97 
No. 88 
ACTINIUM 
Ac =227.02 
No. 89 
THORIUM 
Th =232.12 
No. 90 
PROTOAC- 
TINIUM 
Pa. =231.03 
No. 91 
URANIUM 
U =238.14 
No. 92 
No. 93 NOTE: The following elements have been dis- 
covered in conjunction with the work of the 
Manhattan District. 
NEPTUNIUM. Np, At. No. 93, At. Wt. 239 
PLUTONIUM. Pu, At. No. 94, At. Wt. 239 
AMERICIUM, Am, At. No. 95 
CURIUM, Cm, At. No. 96 
NEW ELEMENTS 
TERBIUM 
Tb. =195.2 
No. 65 
LUTECIUM 
Lu. =175.0 
No. 71 
GADOLINIUM 
Gd. =157.3 
No. 64 
YTTERBIUM 
Yb, =173.5 
No. 70 
ELEMENTS NOT CLASSIFIED IN THE TABLE ABOVE 
Fig. 42' 
EUROPIUM 
Eu. =*152.0 
No. 63 
THULIUM 
Tm. =169.4 
No. 69 
SAMARIUM 
Sm. =150.43 
No. 62 
ERBIUM 
Er. =167.64 
No. 68 
ILLINIUM 
11. =146.(?) 
No. 61 
HOLMIUM 
Ho. =163.6 
No. 67 
NEODYMIUM 
Nd. =144.27 
No. 60 
PRASEODYMIUM 
Pr. =140.92 
No. 59 
DYSPROSIUM 
Dy. =162.46 
No. 66 MEDICAL ASPECTS OF AN 
ATOMIC EXPLOSION 
An atomic explosion regardless of its location will 
result in four types of effects, namely: (1) thermal radia- 
tion: C2) air blast; (3) solid blast; and (4) ionizing radia- 
tion. The first three will vary only quantitatively from 
similar blast effects of other forms of explosion, all quite 
familiar and frequently encountered in pre-atomic warfare. 
The radiation effect, however, is something which is new, 
X-radiation being the nearest prototype with which we are 
at all familiar. This offers but a poor conception of the 
problems which arise and of the biological changes which 
follow “total body radiation” with neutrons, beta and gam- 
ma rays and alpha particles from the ingestion or inhala- 
tion bs radioactive materials. 
In the event of an air explosion, the radioactive cloud 
rises quickly to a height of forty to sixty thousand feet 
and is diluted and spread over a very considerable area 
so that the residual effects in and about the area of the 
explosion are of relatively little importance. In the under- 
water type of explosion, however, the radioactive material 
is almost entirely confined within the rising column of 
Water and is, shortly thereafter, deposited in the immed- 
iate vicinity of the blast together with the radioactivity 
which has been induced in the water and in the marine 
life. It can readily be seen that the latter condition im- 
poses a hazard of almost unbelievable proportions from 
radioactivity alone and to this must be added the fact that 
the unfissioned material of the bomb' as well as many of 
the fission products have extremely toxic properties. 
It will be necessary, therefore, for the medical offi- 
cer to have information not only of the biological effects 
which are produced and the possibilities of treatment, but 
also the methods of detection of the hazard, means of pro- 
tection and avoidance, safety allowances of exposure, and 
of his role and responsibility in the varied aspects of the 
problem. Below, all of these will be considered. 
86 POINT 
SOURCE 
D/RECT RADIATION 
(POINT SOURCE- /?.) 
Fig. 43 
TOTAL BODY RAD/AT1 ON (EXTENDED SOURCE )(/3, r) 
A WHEN ENERGY /S WEAK. OR WHEN ONLY/3 RADIATION, TH/S IS 
NORE /NPORTANT THAN THE CASE OF H/GH ENEROY'FPAD/A- 
T/ON FRON THE SURFACE. 
B LY/NG ON THE DECK NAY TURN A SLIGHT HAZARD INTO A 
SERIOUS ONE UNDER CONDITIONS OF A ABOVE. 
Fig. 44 Hazard of Explosion 
It has been found that it is rather difficult to convey 
adequately and briefly a working understanding of the radio- 
logical hazards of atomic explosion and the peculiar pat- 
terns these hazards present. In an attempt to overcome 
this difficulty, a rather crude series of diagrams has been 
prepared to picture graphically for the beginner many 
different forms in which the hazard may appear. 
In the first place, it is desirable to point out that 
there are two main types of radiological hazard and that 
these two differ markedly in their basic characteristics, 
each requiring an entirely different approach. This may 
be confusing unless clearly differentiated in the mind of the 
individual. 
The first type of hazard is that of external body rad- 
iation. This is similar to that which would be encountered 
if the individual were exposed to a giant X-ray machine 
except that the rays would, in the first instance, be rad- 
iating in all directions instead of from a single source. 
This form of hazard is well known in medicine and in cer- 
tain of the industries. Certainly, the atomic bomb has 
provided no new information as to the qualitative charact- 
eristics of this type of radiation. On the other hand, never 
before has this type of radiation been encountered when it 
consisted of such a variety of forms, with such a wide 
range of energies, and covering such a wide range of ef- 
fectiveness. It is impractical, therefore, for one to think 
of this form of external radiation as directly comparable 
to the hazards of an X-ray machine, although the concepts 
of protection which have been developed and applied to X- 
rays are applicable to certain aspects of the hazards of 
atomic explosion. There are essential differences relating 
to magnitude, range, and in the case of an under water burst, 
contamination of large areas by radioactive materials. 
To describe this difference in the pattern of the haz- 
ard, the radiologist speaks of this as the “geometry’’ of 
the radiation. This is of great importance in the under- 
standing of the characteristics of radiation dangers. The 
maximum permissiable exposure limit of 0.1 roentgen per 
24 hour day is based upon “total body radiation”. If ex- 
posure is from a point source and the area of exposure 
greatly reduced, as to a few square centimeters, several 
thousand roentgens may be administered without danger of 
general injury to the patient. This is not infrequently done 
in the case of small localized lesions. However this is a 
localized and carefully controlled application of radiation, 
and does not permit even the slightest relaxation of our 
88 respect for the tolerance limits which have been establish- 
ed for purposes of safety. When an individual receives 
total body radiation of 400 roentgens, even over a period 
of time, it is almost certain that that individual will die. 
Three hundred roentgens is likely to be a fatal dose. -Be- 
tween one hundred and three hundred roentgens, serious in- 
jury is almost certain to occur. Between twenty-five and 
one hundred, there will be some injury, although probably 
not enough to seriously cripple or endanger the future 
health of the individual. On the other hand, we do not know 
at the present time what effect these smaller doses may 
have on gonadal tissue or what far-reaching genetic changes 
may be produced. Below twenty-five roentgens, it is un- 
likely that any injury of importance will occur, although 
many well informed radiologists feel that doses as small 
as ten roentgens may have some subtle injurious effect. 
Certain factors have an important bearing on the na- 
ture and extent of the injury sustained. They are primar- 
ily characteristics of the radiation rather than of the in- 
dividual, and include: 
(1) The “quantity delivered” which is usually ex- 
pressed in total roentgens of exposure. Roughly, the great- 
er the amount of irradiation, the greater the absorption by 
the tissue and the greater the resultant injury. 
(2) The “hardness” of the ray has a bearing on 
the ability of the ray to penetrate. In general, the shorter 
the wave length of the ray the more penetrating it is and 
the greater the depth dose and the consequent injury to 
vital organs. 
C3) The “duration of exposure” is also a factor 
and it may be that a large dose given, or received, in a 
very short time will not be as fully absorbed as a smaller 
amount received over a longer period of time. 
(4) The “size of the area irradiated”. The larger 
the area exposed to irradiation, the greater the possibility 
of damage. 
(5) In general, gamma rays and neutrons are more 
penetrating and damaging to internal structures than beta 
rays. 
(6) The greater the energy of the ionizing radia- 
tion, the greater the resultant damage. 
In chemical warfare, CT is a symbol used to indicate 
the toxicity of a compound. It is not directly applicable to 
radiology but does make a convenient aid in evaluating 
89 grossly the seriousness of a hazard. In the expression, 
C represents the concentration of the poisonous agent and 
T the time or duration of exposure to the agent. This is 
demonstrated in Figure (45). The effective dose is repre- 
sented by the square area of the rectangle and,in general, when 
a lethal dose or an injurious dose is mentioned, it refers 
to this combination of time and concentration and is expre- 
ssed in terms of total dosage. Thus, for a lethal dose, the 
concentration of a gas must be five times greater if expos- 
ure time is five minutes than would be required if expo- 
sure time were twenty-five minutes. 
/EXTERNAL RA D/A T!ON 
CONCENTRATION 
(C) 
CHEMICAL SYMBOL FOR TOXIC DOSAGE (CT 
COMPARABLE TO TOTAL/RADIATION DOSAGE. 
EXTERNAL 
t/me (r) 
Fig. 45 
A very comparable situation exists in total body rad- 
iation. There is a great deal of evidence to show that the 
“total amount of radiation received’’ is the factor which 
decides the severity of the resultant damage and that the 
factor, that is, the period of time over which this dosage 
was absorbed, is of lesser importance. This is, of course, 
not mathematically true in extreme cases where very min- 
ute doses might be absorbed over a period of years and 
no damage occur although the total dose be considerable, 
but for purposes of radiological safety, it must be consid- 
ered as a true and reliable working principle. 
Internal Radiation 
A second type of irradiation hazard is quite different 
from that of the external radiation described above. It is 
a type of hazard which is encountered in the radium indus- 
try, particularly in the radium dial painters’ laboratory. It 
is an internal poison comparable in many ways to any chem- 
ical type of internal poison, particularly by the heavy met- 
als. It has long been known that radium, ingested or in- 
haled, even in dilute form and regardless of its chemical 
composition, tends to enter the blood stream and deposit 
90 in the bones. In some of the bones, very little harm may 
result but when it settles in the blood forming marrow, the 
characteristic picture of radium poisoning results. The 
same picture may result from the ingestion or inhalation 
of particulates of the fissionable material or the fission 
products of the atomic bomb. 
DECAY CURVE 
INTENSITY 
TIME 
INFLUENCE OF NATURAL RADIOACTIVE DECAY OF FISSION 
PRODUCTS/CONCERNING CHANGE IN HAZARD 
AND FISSIONABLE MATERIAL 
Fig. A6 
DECAY CURVE 
WEATHERING EFFECTS 
INTENSITY 
TIME 
INFLUENCE OF WEATHERING ON THE CHANGE IN HAZARD. 
WEATHERING TENDS TO REDUCE THE HAZARD BY REMOVAL OF THE 
MATERIAL FROM THE CONTAMINATED SITE TO ANOTHER SITE. 
Fig. A7 
91 The alpha particles which are emitted by these mater- 
ials are extremely high energy particles and, although they 
have a very limited range and low powers of penetration, 
they are capable of producing some of the most insidious 
and destructive of the radiation injuries. It is important to 
re-emphasize that, from a standpoint of external radiation, 
the alpha particle has an almost negligible effect. It is 
only when the alpha emitting materials are absorbed by the 
body that destructive effect becomes important. 
This has added significance when it is remembered 
that alpha particles are very difficult to detect. Their pre- 
sence is therefore easily overlooked or erroneously disre- 
garded by the uninformed. There is at present no instru- 
ment suitable for field use which will detect alpha particles. 
Instruments for the detection of gamma and beta presence 
will be later described. It may be pointed out here, how- 
ever, that under field conditions, it may be necessary to 
calculate the amount of alpha hazard present from the mea- 
surement of beta and gamma radiations. An under standing 
of this may be obtained by referring to Figure (46; which 
is a characteristic decay curve. It will be noted that the 
intensity of radiation falls off with time. By using certain 
information supplied by radio-chemical analyses, determin- 
ing the intensity of beta and gamma radiation at any given 
time, and referring back to the curve, it is possible to 
estimate the alpha intensity at that particular time and place 
This is a time consuming and laborious method requiring 
special techniques and it is also true that there may be 
some discrepancies in the curve as shown in Figure (47). 
Further, due to natural weathering and the transference of 
contaminated material from one place to another, it is pos- 
sible for the curves to be given an acceleration in their 
downward course. The material which is likely to be the 
most resistant over a long period of years consists of cer-. 
tain long life fission products and alpha emitters. One can 
readily understand, therefore, the need for particular care. 
Protection against this hazard is accomplished by 
avoidance only. Inhalation can be avoided by the employ- 
ment of suitable oxygen rescue breathing apparatus or gas 
masks with appropriate filters. Access through the skin 
can be prevented by wearing clothing wliich prevents con- 
tact of the particulates with the skin, by measures of hyg- 
iene, and the care of possibly contaminated wounds. One of 
the most important principles- is the development of a proper 
understanding of what the hazard is, its peculiarities and its 
characteristics. Only on such a foundation can an approach 
be made to the solution of the safety problems which this 
form of hazard presents. 
92 NAN IN THE OPEN 
a DIRECT RADIATION. ( s?). 
J>. SCATTERED RADIATION. ( r; n). 
Fig. AS 
EXTERNAL RADIATION 
NAN /N BUILDING (TOTAL BOO! RADIATION) 
a. DIRECT RADIATION ( Y;/}) 
h. SCATTERED RADIATION ( r,n). 
Fig. U9 
The Geometry of Radiation 
At the time of atomic explosion, there is emitted an 
intense radiation which includes beta and gamma rays and 
neutrons together with radiant heat and light. Effective 
ranges of these factors differ, but in each the intensity de- 
creases with the distance from the source. The range to 
which neutrons are emitted is less than the range of gamma 
rays. The infra red and ultra violet rays, in intensities 
sufficient to injure skin at least temporarily, extend to a 
distance somewhat beyond that of the gamma rays. The di- 
rect radiation which occurs at the time of explosion is 
shown graphically in Figure (48) which indicates the type 
93 
7803!)H 0—48——7 of radiation to which an individual in the open would be ex- 
posed if within the range of the gamma rays. In this type 
of exposure, the side of the individual exposed to the 
direct rays would be effected. Flash burns and eventual 
loss of hair in those individuals who survive would be un- 
ilateral. Practically, this theoretical purity of exposure is 
almost impossible since there would always be some sec- 
ondary emission of rays from the ground and from nearby 
objects. This effect is known as 4 scattering” and is most 
characterlsticalv seen inside a building. (See Figure (49). 
The gamma rays entering the building would be scattered 
in such a way that the total body radiation would be con- 
siderable and in the aggregate would constitute an impor- 
tant disabling and killing agent. It would be possible for 
an individual so exposed to accumulate lethal exposure as 
a result of overall radiation without having sufficient local 
exposure to produce loss of hair. An individual in this 
position would, of course, be almost completely protected 
from infra red and ultra violet rays. 
At the time of explosion, a “ball of fire” is formed, 
represented by the central circle in Figure C50)'. This 
EXTERNAL RADIATION 
ASCENT OF 
BALL OF FIRE- 
DIRECT RADIATION FROM "BALL OF FIRE" 
IN ITS ASCENT. ( n n) 
Fig.*50 
ball of fire continues to emit radiations for a matter of 
several seconds during which time it is rising from the 
original point of detonation. In a relatively short time, it 
reaches a height from which none of the radiations reach 
the earth. Therefore, there is a moving source of radia- 
tion which, as it goes skyward, subjects the individual on 
the ground to continuous exposure during the time that it 
is in range of the individual. The total effect will be, 
94 then, a combination of the initial “instantaneous” radiation 
of extremely short duration, and the “delayed” radiation 
which lasts for several seconds. 
Induced Radioactivity 
As a result of neutron bombardment, certain elements 
become artifically radioactive -and, following the atomic 
explosion, constitute what is termed “induced activity”. 
One form of induced activity is illustrated in .Figure (51). 
EXTERNAL RADIATION 
(FROM RESIDUAL RADIOACTIVITY) 
NEUTRONS 
NEUTkCks 
\ \ 
cl INDUCED RADIOACTIVITY IN SEA WATER i/9. Jr) 
h. INDUCED RADIOACTIVITY IN SHIPS i/Q,*). 
Fig. 51 
In sea water there are several elements including sodium, 
chlorine, and iodine, which may become radioactive in this 
manner. Of these, by far the most important is sodium. 
It emits both beta and gamma rays. It has a relatively 
short half life, however, so that in a few days there is 
little hazard from an external radiation standpoint. Certain 
metals, particularly those containing copper, bronze, or 
manganese may be made radioactive. Also, certain soils, 
drugs (notably Salvarsan), table salt, and even on occasion 
the gold fillings of teeth may become artifically radioact- 
ive and constitute a hazard. 
The presence of radioactivity in the soil is of parti- 
cular interest and importance because it is possible, by 
the use of instruments currently in use, to detect and mea- 
sure this activity from the air at a height of over a thou- 
sand feet and thus chart a geometrical outline of the area 
of contamination together with the intensity. This is of 
particular importance over land areas but is also impor- 
95 COMBINATION EXTERNAL L INTERNAL RADIATION HAZARD 
(FROM RESIDUAL RADIOACTIVITY) 
(FISSION PRODUCTS) 
JT CAN BE MEASURED AT SEVERAL 
THOUSAND FEET EARLY 
FISSION PRODUCTS 4 RADIUMA 
LIKE MATERIAL IN SEA WATER. 
TARGET VESSELS 
TARGET VESSELS AND SEA WATER 
RESIDUAL RADIOACTIVITY RESULTING FROM THE DEPOSITION OF FISSION PRODUCTS IN 
AN UNDERWATER EXPLOSION. 
F±g. 52 
taut in marine survey where activity has been induced in 
the sea water and in both plant and animal marine life. 
Fall Out 
More important than the induced radioactivity, how- 
ever, is the contamination which occurs due to the fall- 
out” of radioactive materials from the atomic cloud. This, 
as has been previously noted, is of almost unbelievable 
seriousness in the case of an underwater blast. The pat- 
tern of fall-out will vary considerable with wind and wea- 
ther conditions as well as the with the location of the 
detonation. Humidity, rain, and wind will effect the height 
to which the atomic cloud will rise hs well as the rapidity 
and location of the radioactive deposit. In the case of 
under or over water explosion, tides and currents will 
effect the speed with which the contaminants will be spread, 
Fall-out contamination of a surface ship is illustra- 
ted in Figure (52). Contamination of this type presents 
a combination of internal and external irradiation hazard to 
personnel and consists of unfissioned bomb material as well 
as fission products. Early following contamination, exter- 
nal body radiation will be of most serious importance as 
most of the fission products have relatively short half 
lives. However those products having long half-lives will 
continue to be important internal radiation hazards long af- 
ter the initial intensity has subsided. 
Figure (53) iHustrates the contamination of a ship’s 
hull as the result of sailing in contaminated waters. This 
type of contamination wiH first be noted on the under-water 
9b body surface of the ship, particularly around the green sea 
growth at the water margin. Crustaceans and algae have 
been found to have the faculty of absorbing and concentra- 
ting the radioactivity from the water and barnacles become 
particularly “hot”. It will soon be found also that salt 
water lines and especially condenser lines will be radio- 
active. The scale in the lines apparently concentrates the 
activity in much the same manner as does the marine 
growth. 
COMBINATION EXTERNAL AND INTERNAL 
RADIATION HAZARD 
(FROM RESIDUAL RADIOACTIVITY) 
FISSION PRODUCTS 
SALTWATER LINES. 
CONDENSERS- ETC. 
UNDERWATER BODY 
NON-TARGET SHIPS 
F1 g. 53 
COMBINATION EXTERNAL £ INTERNAL RADIATION HAZARD 
FROM RESIDUAL RADIOACTIVITY 
FISSION PRODUCTS 
WATER SURFACE 
PLANT LIFE 
SHIP 
MARINE LIFE 
RESIDUAL RADIOACTIVITY 
a. EARLY FISSION PRODUCTS ARE PRETTY WELL SCATTERED THROUGHOUT 
THE WATER AND ON THE SURFACES OF THE SHIPS. (/3. T, OL). 
b. AS TIME GOES ON FISSION PRODUCTS ARE CONCENTRATED IN MARINE LIFE 
AND IN ORGANIC MATERIAL IN THE BOTTOp 
LASOON BOTTOM 
Fig. 54 
97 Figure (54) indicates the contamination of the sea 
floor. In shallow areas or in diving operations, this may 
become an important factor. The activity will be largely 
confined to sea growth or bottom mud in most cases, since 
the tides and currents will spread most of the actual water 
contamination both direct and induced. 
Figure (55) and (56) indicate land contamination at a 
distance from the original explosion and demonstrate the 
importance of aerography and terrain in the distribution of 
the fall-out. Figure (55) gives a graphic picture of what 
occurred in New Mexico fifty miles northeast of the point 
of detonation. The radioactive matter was in the form of 
vaporized sand to which the fission products adhered. This 
CLOUD 
FALL /OUT 
///'// 
NEW MEXICO DESERT 
FINE PARTICLES OF MATERIAL CONTAMINATED WITH FISSION 
PRODUCTS FELL OUT OF CLOUD ARISING FROM TOP OF EXPLOSION 
COLUMN AFTER IT HAD TRAVELED SO MILES TO THE NORTH EAST 
IT WAS NOT A SERIOUS HAZARD ON THIS OCCASION. 
Fig. 55. 
\W\' \ \\' 
HILL 
CO/ITNIlRATElr 
AREA 
HILL 
FINE PARTICLES OF MATERIAL CONTAMINATED WITH FISSION PRODUCTS 
FELL OUT OF CLOUD ARISING FROM THE EXPLOSION COLUMN AFTER 
IT HAD TRAVELED A FEW MILES TO THE EAST OF NAGASAKI. IT 
WAS NOT A SERIOUS HAZARD ON THIS OCCASION. 
NAGASAKI 
P4*. 56 
98 material fell-out into an area occupied by a herd of Her- 
ford cattle which later developed white, spotty dappling of 
their red coats due to the local effects of the particulate 
radioactivity on the individual hair follicles. Figure (56) 
represents the deposite of the fall-out at Nagasaki. Note 
that the cloud passed over two hills and traveled several 
miles before depositing in a small area of the second hill 
not far from a water reservoir. 
Contamination 
An additional type of contamination has thus far not 
been mentioned but is nevertheless of utmost importance. 
Actually, it consists of re-contamination and is the result 
of the carrying in of radioactive particles to otherwise 
“clean” areas. Personnel who have been directly contam- 
inated and those who have had access to the contaminated 
areas are likely to carry this contamination on their feet, 
hands, or clothing, or on articles of any kind which they 
have attempted to salvage from the contaminated area. This 
must be avoided if at all possible and necessitates the ' 
wearing of protective* clothing by rescue parties, the re- 
moval of “hot” clothing and, if necessary, repeated bathing 
before coming from a contaminated to a clean area. Ex- 
treme vigilance and careful and constant monitoring is es- 
sential. 
Industrial Problem 
The above type of contamination is encountered under 
conditions other than actual atomic explosion and is im- 
portant to the medical officer in his role as an industrial 
hygienist. If atomic power plants come into use by the 
service or if in the future atomic power is used in ships 
or in aircraft of any variety, this consideration will be 
come increasingly important. Supervision of measures to 
prevent undue exposure of personnel to the toxic or radio- 
active effects of fissioning material or fission products will 
be the province of the medical department. This will nec- 
essitate a general knowledge of the implications of radio- 
logical safety on the part of all hands plus very specialized 
and detailed knowledge of certain of its phases by a fewer 
number. 
* NOTE: The word "protective" is not meant to imply protec- 
tion against radioactivity but only protection of the 
individual against contamination with radioactive 
materials. 
99 EFFECTIVE RANGES, AND THE ESTIMATION OF PRO- 
BABLE CASUALTY PRODUCTION AT THE TIME OF AN 
ATOMIC BOMB EXPLOSION 
For purposes of planning, the approximate ranges 
within which injuries to personnel could be anticipated for 
the various types of hazard, are given. 
When the bomb is detonated in the air as at Nagasaki 
and Hiroshima or on the surface of the ground, injuries 
may be expected within these ranges: 
Blast (direct, unshielded) 
— 1300 - 1500 yards 
Blast (indirect effects) 
Radiation (instantaneous): 
3,000 yards 
Infra-red 
— 3,000 yards 
Ultra-violet — 
Visible light 
—10,000 yards 
Ionizing radiations 
Neutrons 
— 700 yards 
Fission products 
- Wide distribution in air 
Non fissioned material 
— Wide distribution in air 
For planning purposes, many casualties would be an- 
ticipated among personnel exposed in the open within 3,000 
yards of an air burst bomb. While ordinary buildings 
would provide some protection against flash burns, they 
would provide relatively little protection against ionizing 
radiations and might increase the chances of indirect blast 
and fire casualties due to falling and burning of buildings. 
An estimate of the number of casualties in an air burst or 
surface burst would be 1/3 immediate deaths, 1/3 early 
deaths and 173 serious casualties requiring much medical 
attention. This would include all personnel within the 3,000 
yards range. 
In no instance does this take into account the adverse 
psychologic effects to personnel which can certainly be es- 
timated to be serious and which may indeed prove to be a 
major concern. This will depend very much on how well 
these effects can be minimized by adequate indoctrination, 
smooth organization, and leadership. It is impossible to 
make a good estimate of this phase of the anti-personnel 
effect. 
100 FIELD INSTRUMENTS FOR 
THE DETECTION OF ION- 
IZING RADIATION 
GENERAL 
Instruments 
The detection and measurement of high energy ioniz- 
ing radiation depends entirely upon suitable instruments and 
photographic film. Without these, even intense radiation 
will not be recognized until serious damage has been done. 
It is important, therefore, that the monitor have a thorough 
understand of the principles of operation and the limitations 
of available instruments. 
The three radiations, alpha and beta particles and 
gamma rays, cannot be detected and measured with equal 
facility. Alpha particles, because of their short range, will, 
not be measured' with the usual partable instrument. Ioni- 
zation chambers with windows of thin mica or stretched 
nylon 0.0001 inches thick will measure alpha particles, but 
a dependable field instrument incorporating this feature has 
not been developed. The proportional counter will also 
measure alpha, but it can hardly be considered a field in- 
strument because of its size. Beta particles and gamma 
rays can be determined with a single Geiger-Mueller tube 
instrument; by opening a window in front of the tube both 
radiations will be measured, but only gamma rays will 
penetrate with the window closed. Most portable ionization 
chambers are designed to measure only gamma rays since 
durability would be lost if thin walls were used which 
would permit beta particles to penetrate into the ion cham- 
ber. The same is true of electrometers and electroscopes. 
The essential requirements of a field instrument are 
portability, ruggedness and dependability. It must be sim- 
ple in operation so that personnel can be rapidly trained 
in its use. It must be so designed that repairs and 
replacement of parts can be accomplished in the field. The 
instruments at present available for survey work fall into 
four groups. 
101 Following are some of the general characteristics 
of existing instruments: 
(a) Geiger Counters. 
Geiger counters have been designed for field 
use as small as 250 cubic inches and with a weight of only 
2 to 4 pounds. 
This instrument contains its own portable batteries. In 
most designs ear phones are provided for audible detec- 
tion in addition to a meter for scale readings. The scale 
has a range of from O.OOlr to 0.5r per 24 hours but by 
means of the ear phones it is possible to measure intensi- 
ties about 1/3 or 1/5 as great. Thus this instrument is a 
rate meter for measuring low levels of radiation. It is 
designed with a window so that when the window is closed, 
only gamma rays are detected, and when the window is 
open both beta particles and gamma rays can be measured. 
Gf-iger Counter in Use 
102 (b) Ionization Chambers. 
Ionization chambers have been developed for 
field use with a volume of about 1 cubic foot and weighing 
17 to 20 pounds. 
A--lon Chamber 
B—Geiger Counter 
Some of the present models have three scales covering a 
range for 0.1 to 200 R per 24 hours so that this instru- 
ment is used when high intensities are being measured. 
The present chambers are designed to measure only gamma 
radiation. 
(c) Electrometers. 
In contrast with the G-M counters and ioniza- 
tion chambers which are ratemeters, electroscopes are used 
tt> measure accumulated radiation exposure. A small pen- 
cil like electroscope known as a pocket dosimeter has been 
found exceedingly practical for field use. Since this instru- 
ment does not contain an integral voltage supply, it must 
be charged before use. Dosimeters are easily constructed 
and are designed to measure total exposure of about 0.3 
roentgen, but if higher exposures must be measured, spec- 
103 ial models can probably be developed. Because it can be 
easily carried in a pocket, this instrument is extremely 
useful in the field since it leave the hands free for other 
purposes. 
A—Dos ime ter 
B—Survey Meter 
C—Charger and Pencil Electroscope 
In addition to this, small portable Lauritsen 
electroscopes have been designed. However, for most 
field work the small pocket dosimeter is Recommended. 
When an electroscope which has been out of use for some 
time is charged, a rapid discharge will be frequently obser- 
ved. This is caused by a generation of part of the charge 
into an insulator. To eliminate this the instrument should 
be given a preliminary charge a day or more before actual 
use. 
(d) Film Badges. 
A valuable supplement to the ratemeter and 
dosimeter is the film badge. Photographic film is sensi- 
tive to beta particles and gamma rays; in addition, by 
treatment of the emulsion with dye and addition of boron, 
it can be made sensitive to alpha particles and neutrons. 
The film, in the form of a badge, about .1” x 2”, can be 
104 worn by personnel or placed in areas where radiation 
exists or may be expected. It also contains a lead cross 
to intensify the gamma radiation. It provides an accurate 
and permanent record of total exposure and therefore may 
be regarded as a dosimeter. It is easily handled and cal- 
ibrated and requires no complicated electrical equipment. 
These are only a few of the tools of the 
“Monitor” whose duty it is to detect and report the hazards 
their location and intensity. The electroscope and the film 
badge are worn by personnel likely to be exposed to ioniz- 
ing radiation and measure the total radiation to which the- 
individual has been exposed during the period they have 
been worn. The electroscope may be read directly at any 
time whereas the film must be processed by methods sim- 
ilar to that used in developing X-ray films. The density of 
the film is proportional to the amount of exposure it has 
sustained and this is accurately measured by photoelectric 
methods using a so-called “densitometer”. The electro- 
scope and film badge are normally worn simultaneously and 
act as a check on each other. 
There are many other types of detectors but most 
of them are not field instruments. Since monitoring is not 
usually the duty of medical personnel, other types will not 
be described here. More detailed association with them 
and some practice in the use of the field type of instrument 
ments will be reserved for more advanced and personal- 
ized forms of instruction. 
CALCULATION OF RISKS IN CONNECTION WITH RADIO- 
LOGICAL HAZARDS. 
In the event of atomic warfare, commanding officers 
may be forced to accept certain calculated risks in a 
manner similar to that of other dangerous military opera- 
tions. 
In this respect the problem is essentially no differ- 
ent than in operations not involving radiological safety, 
certain techniques make the calculation of radiological risks 
somewhat more satisfactory in certain respects. This 
calculation can be employed only in connection with the en- 
try into and the occupation of contaminated area. 
The basis for the calculation of the risk will be: 
(a) Radiological survey of the area of the in- 
individual site. It may apply to collective safety 
as far as a unit of troops is concerned or the 
specific hazard to which a rescue party may be ex- 
posed in the conduct of its mission. 
105 (b) The consultation of the Radiological Safety- 
Officer with the Radiological Health Officer and the 
presentation to the commanding officer of the re- 
commendations arrived at from the analysis of the 
radiological survey. 
(c) A scale indicating probable injurious ef- 
fects of various doses of exposure. 
There are many factors to be considered; 
Time After Detonation 
Radioactivity will be most intense shortly after the 
detonation and will decrease markedly the first day, gener- 
ally in accordance with a regular decay curve, as previous- 
ly noted. The residual effects from an air burst will be 
practically nil. In the case of the water burst, however, 
entry into or occupation of the areas of contamination would 
require a particularly careful calculation of the risk be- 
cause of the greater inherent danger of high and persistent 
residual activity. Several months after detonation of this 
type, the danger of internal radiation is likely to be more 
serious than the hazard of external radiation because of 
the decay rate of the latter type. The estimation of the 
alpha hazard is much more difficult (as previously noted) 
and requires very special techniques. A number of spec- 
ialists and a great deal of time are required to make these 
estimates. 
Reliability of RadSafe Organization 
Unless survey data is reliable, proper calculations of 
risks cannot be made. This requires that good judgement 
be employed not only in assessing the intensity of the haz- 
ard but also in interpreting the reliability and the suit- 
ability of the data presented. This will necessitate the 
employment of personnel who are properly trained and who 
are technically and personally reliable. Instruments must 
be reliable and their use must be in accordance with 
proper proceedure. 
In the absence of any or all of the above, the prob- 
lem of calculating the risk may be insurmountable. In this 
event, it is best to assume conditions of relative safety if 
it is a high air burst of the Japanese type; if it is a sur- 
face or water burst of the type seen in New Mexico or at 
Bikini it should be assumed that conditions are so serious 
as to contradict entry or occupation. In the latter situa- 
tion, only the gravest and most vital mission could be en- 
tertained since the risk would be so great as to put the 
venture in the nature of a suicide project. 
106 Dosage of Exposure and How Employed in Calculating 
Risk 
The importance of the “time and concentration” fac- 
tors, and the importance of “total amount of radiation rec- 
eived” in total body radiation‘has already been pointed out. 
It is worth while, also, to repeat that 0.1 r daily is the 
maximum total radiation which is considered permissable. 
The total dosage possible, can be calculated by measuring 
the intensity of radiation at a given site or in a given area, 
and introducing the time factor.' From this the allow- 
able time in that particular area, can be determined. (See 
table p. 108). 
For example, the intensity at site (a) according to the 
reading of a reliable meter is 100 r/day. In 24 hours, an 
individual would receive 100 r; in 12 hours, 50 r; in 1 hour, 
4r; in 15 minutes, 1 r, etc. Thus an individual would rec- 
eive ten times the maximum allowable dose of exposure in 
fifteen minutes in area (a). 
Low Grade Hazard as in Normal Safety 
Operations 
In a controllable situation, the pocket dosimeter 
(electroscope) and the film badges are worn. If either or 
both of the devices should indicate that the individual wear- 
ing them had been exposed to 0.4 roentgens during any 
given working day, it would be necessary to remove him 
from any area containing radiation hazards for a minimum 
period of four days. In cases of marked over exposure, 
the foHowing table may be used to estimate the result as- 
suming that the exposure has been accumulated over a rel- 
atively short period such as several weeks: 
0.1 r Maximum daily permissible dosage 
0.1 to 10 r Relatively little risk. 
10 to 25 r Some injury likely but probably 
not incapacitating. 
100 to 300 Serious injury, some deaths prac- 
tically certain but may be delayed. 
300 to 600 Serious injury or death certain, 
very serious incapacitation, some 
may linger for weeks or months 
requiring extensive medical at- 
tention and even then die. 
600 to 1,000 r Death certain, iisually in first 
24 hours. 
above 1,000 r Death certain, usually in a few 
hours. 
107 INTERPOLATION OF METER READINGS INTO MAXIMUM 
WORKING TIMES 
Personnel working in contaminated areas should not 
stay in these areas any longer than the time indicated in 
this table. 
Column 
No.l 
Column 
No. 2 
Maximum 
allowable length of time 
for personnel working 
in Radioact- 
ive areas 
of intensity r/day shown 
in Column No.l. For every 24 hour 
periods. 
Working 
Point 
Hours 
Minutes 
Second 
100 
0 
1 
26 
90 
0 
1 
36 
80 
0 
1 
48 
70 
0 
2 
3 
60 
0 
2 
24 
50 
0 
2 
53 
40 
0 
3 
36 
30 
0 
4 
48 
20 
0 
7 
12 
10 
0 
14 
24 
9 
0 
16 
00 
8 
0 
18 
00 
7 
0 
20 
34 
6 
0 
24 
00 
5 
0 
28 
48 
4 
0 
36 
00 
3 
0 
48 
00 
2 
1 
12 
00 
1 
2 
24 
00 
0.9 
2 
40 
00 
0.8 
3 
00 
00 
0.7 
3 
25 
00 
0.6 
4 
00 
00 
0.5 
4 
48 
00 
0.4 
6 
00 
00 
0.3 
8 
00 
00 
0.2 
12 
00 
00 
0.1 
24 
00 
00 
Column No. 1 
= Values from calibrations curves of instru- 
ments. 
108 Internal Body Radiation 
The maximum permissable limit of radium-like mat- 
erial which may be absorbed, as established by the Man- 
hattan Engineer District Scientists, is one (1) MICROGRAM 
in an entire life time. 
It will be noted in the pages which follow that there, 
is a moderate amount of repetition. This is intentional. 
Certain of the medical aspects are of such importance and 
certain factors so easily neglected that the added emphasis 
of repetition is considered essential. 
MEDICAL ASPECTS OF AN ATOMIC EXPLOSION 
Thermal Effect 
“Thermal effect” refers to the radiant energy of the 
atomic explosion and does not include the effects of sec- 
ondary fires or explosions which may be the result of the 
detonation. At the instant of the detonation, unmeasurable 
degrees of heat and light are produced. Both the infra red 
and ultra violet rays are capable of producing severe burns 
to the body surface, especially to exposed surfaces of the 
skin. The thermal energy is, however, of very short dur- 
ation and, although it may account for a high proportion 
of the casualties near the center of the detonation because 
of its extreme intensity, a relatively small amount of 
shielding offers considerable protection. Even light cloth- 
ing, especially if glossy surfaced, offers complete protec- 
tion in many cases. Dark colored materials, on the other 
hand, will frequently char or burn. Cases were frequently 
found among the Japanese where the skin was burned in a 
regular pattern depending upon the color and consistency of 
the clothing which has been worn at the time of the blast. 
It has been estimated that between twenty and thirty per 
cent of the fatalities at Nagasaki and Hiroshima were the 
result of flash burns. 
Air Blast 
The primary type of air blast injuries are produced 
by the passage of the pressure wave thru the tissues caus- 
ing actual structural change and injury or death. These 
effects are exerted chiefly at interphases between air and 
solid-as the lungs, the intestines, or the stomach. Except 
for individuals in close proximity to the point of the burst, 
the primary effects are of little importance. At ranges 
where they might be considered dangerous, other factors 
would be of more importance as casualty producers. That 
is, an individual well beyond the limit of danger from pri- 
109 
780393 0—48 8 mary air blast might still receive many times the lethal 
dose or radiation. 
Solid Blast 
The secondary air blast effect is far more important 
than the primary. Casualties are produced by (a) the 
structural collapse of buildings, (b) flying debris, (c) the 
effect of being hurled against solid or semi-solid substances 
All of these injuries would be essentially the same as those 
produced by any heavy air blast. 
In an underwater detonation, the energy transmitted 
thru the water would cause injury to personnel in the water 
at the time and within the concussion range. An individual 
completely submerged is able to withstand many more 
pounds of pressure per-square inch than one partially sub- 
merged. In the latter, rupture of the hollow organs is much 
more likely to occur. The exact range at which this type 
of casualty may be produced is not accurately known but it 
is much less than would normally be imagined, according 
to preliminary reports of research on the subject. In this 
connection it is interesting to note that, in the Bikini test, 
the air containing bladder which is part of the floating 
mechanism of fish, was, in many cases, ruptured and the 
fish were subsequently found on the bottom of the lagoon by 
divers. 
IONIZING RADIATION 
Introduction 
Recently there has been a great deal of interest in 
the biologic effects of the various forms of ionizing radia- 
tions and of neutrons. Individuals exposed to injurious dos- 
ages of these radiations present a variety of clinical con- 
ditions. Important in determining the clinical expression 
of the changes produced is the manner in which the injur- 
ious agent is brought to bear on the individual. Exposure 
of the external surface of the body to penetrating ionizing 
radiations and neutrons causes quite a different set of 
clinical findings from that caused by the injurious effects 
of internal, body radiation. While there is some general 
relationship, among the causative factors in that they belong 
to a group of related and interesting physical incitants, the 
clinical picture as a whole is usually more characteristic 
of the form of exposure than of the intrinsic characteristics 
of the injurious agent. Some of the clinical findings may be 
similar but the clinical picture as a whole is usually quite 
different. The classification presented is an arbitrary one 
and is aimed primarily at providing a terminology suitable 
for clinical diagnostic purposes. 
110 Radiation Sickness is the term used to described the 
illness produced by over-exposure to penetrating ionizing 
radiations and neutrons. Systemic reaction, in this instance, 
arises from exposure of the external surface of the body to 
penetrating radiation. Gamma rays, X-rays and neutrons 
are the more common causative factors. The injurious 
dosage may be received instantly or may be accumulated 
over a period of time. The onset of symptoms may be 
abrupt or insidious. In the acute form, as 'observed at 
Hiroshima, it may be fulminating. In the mild form obser- 
ved after roentgen therapy, the symptoms are usually tran- 
sient. One particularly subtle form sometimes seen is the 
leukemia which occurs in radiologists after years of repeat- 
ed exposure to low grades of accumulating dosage of X-rays. 
Radiation injury is the term employed to describe lo- 
calized injurious effects which are not ordinarily associated 
with any systemic reaction. The incitants may be alpha or 
beta particles, gamma rays and X-rays. The onset is us- 
ually insidious. Some forms of radiation injury may be 
associated with radiation sickness, e.q., epilation of victims 
at Hiroshima. Other examples are precancerous lesions of 
the skin from prolonged and repeated exposure of a partic- 
ular area to radium or X-ray, sterility from exposure of 
testes or ovaries to X-ray,/ and changes in the nails and 
finger prints from prolonged exposure locally to radium or 
X-ray. 
Radioactive poisoning is the term used to describe the 
illnesses which result from radioactive materials gaining 
access to the body. Here, they act as an internal poispn 
producing localized or systemic effects or both. The of- 
fending radioactive poisons are materials which emit nuclear 
particles (alpha or beta) or nuclear radiations (gamma). 
The former in spite of their short range are of particular 
importance in this connection because of their high density 
of ionization. The onset is usually insidious, often subtle, 
and at times indeed it may be years after the original ex- 
posure. In experimental animals relatively massive doses 
can produce an abrupt onset. Examples of radioactive 
poisoning are the radium dial painters illness and poison- 
ing due to drinking radioactive waters. In mining pitch 
blend, lung tumors occur as a result of inhaling radioactive 
dusts. Such lesions may remain localized for a long time 
before systemic effects appear. Radioactive poisoning might 
occur from misuse of radioactive isotopes in attempted 
therapeutic procedures. If the radioactive fission products 
from a nuclear explosions were to gain access to the human 
body in sufficient amounts, it is likely that the individual 
would present much the same clinical picture as that pre- 
sented by the radium dial painters. 
111 RADIATION SICKNESS 
Definition 
Radiation sickness is observed in individuals who have 
been exposed to external body radiation in amounts suffic- 
ient to produce systemic reaction. The clinical findings are 
characteristic. It may be acute or chronic in its clinical 
course. It may be so mild as to cause only a few hours 
illness or so severe as to be fatal within a like period of 
time. 
Incidence 
Radiation sickness was first observed subsequent to 
the introduction of the X-ray machine. As such it occured 
as an accidental affair, due in the main to limited know- 
ledge as to the requirements of safety. As the X-ray and 
the external radiations of radium were used more and more 
in the treatment of various clinical conditions, particularly 
deep seated neoplasms, the outstanding characteristics of 
radiation sickness became more clearly recognized. The 
high incidence of radiation sickness at Hiroshima and at 
Nagasaki provided an opportunity to study radiation sickness 
as it occurred in a large group of people who had been ex- 
posed en masse (a) to total body radiation and (b) to vary- 
ing dosages of such exposure. With the advent of atomic 
warfare, radiation sickness has taken on a new significance. 
Radiation sickness may be encountered in clinical 
practice following deep roentgen therapy or after the use of 
radium. As the consequence of accidental over-exposure, 
it may be observed in personnel employed in industrial 
plants where an external radiation hazard may exist due to 
the use of X-ray or radium in checking of metal castings. 
In experimental laboratories, or wherever they operate 
power X-ray machines, cyclotrons, or a uranium pile, rad- 
iation sickness may follow an accidental exposure to various 
forms of ionizing radiation. 
Etiological Considerations 
Because of the close association of radiation sickness 
with the explosion of an atomic bomb, there is a fairly 
widespread impression among, non-medical individuals that 
radiation sickness is a new disease entity born with the 
atomic bomb. Such is indeed not the case. Radiation sick- 
ness has long been recognized as a clinical entity by the 
roentgenologists. The exact mechanism by which ionizing 
radiations and neutrons produce injury in living cells is not 
known. Nor do we have specific therapeutic measures which 
112 can be employed to counteract the injurious effects of ir- 
radiation within tissues. On the other hand there is nothing 
particularly mysterious as far as the clinical manifestations 
of radiation sickness are concerned. Many illnesses are 
not so easily recognized or so well understood. 
Intensive studies conducted on the casualties at Hiro- 
shima and at Nagasaki, while yielding little new informa- 
tion which may be regarded as basic in character, neverthe- 
less, have provided valuable information which confirms, or 
adds to, our previous understanding of radiation sickness. 
Gamma radiation, quite similar in nature to the X-ray, 
was the most significant form of radiation, although it is 
not unlikely that the neutron radiation was also of greater 
importance than may now appear. Some individuals were 
exposed to a combination of gamma rays and neutrons, and 
some to infra red and ultra-violet energy as well. No one 
was exposed to neutrons alone. Although we do have con- 
siderable information on the effects of both fast and thermal 
neutrons on living tissue, we do not have as much informa- 
tion as we have on radiation by gamma ray and X-ray. 
Extrinsic Factors Influencing Radiation Exposure 
Radiosensitivity - As far as the individual is concern- 
ed there are certain intrinsic factors which determine the 
degree,, or pattern, of cellular response to a given form 
and dosage of radiation. Tissues particularly susceptible 
to radiation injury are described as being radiosensitive 
and those least sensitive as radioresistant. 
There is considerable variation in radiosensitivity 
among species organs, and cells. 
(a) SPECIES - The guinea pig and the rat are 
much more sensitive and the goat about equally sensitive 
with man. Fish are much less sensitive to radiation than 
man. As a consequence, the results of animal experimen- 
tation are not always directly applicable to man. 
Cb) ORGANS - The lymph glands, the bone marrow, 
the testes and the ovaries are the most sensitive organs. 
The hair follicles are more sensitive than the surrounding 
layers of skin. The brain, characterized by an extremely 
highly organized cellular tissue, is peculiarly resistant to 
radiation, the muscle tissue is somewhat less resistant. 
(c) CELLS - For a given type of cell, the more 
immature it is the more radiosensitive it tends to be. The 
most sensitive cells in decreasing order of sensitivity are 
113 lymphocytes, germinal cells of testes and ovaries, granulo- 
cytes, platelets and erythrocytes. The formed elements 
within the circulating blood are slightly less sensitive than 
those within the hematopoietic tissues. Somewhat less sen- 
sitive than any of the preceding cells are certain epithelial 
cells. As a consequence cytologic blood studies provide 
the earliest and most reliable indices of the clinical state. 
IONIZATION-IN LIVING TISSUES 
Penetrating Radiations 
It is customary to refer to hard electromagnetic rad- 
iations and neutrons as penetrating radiations. Gamma rays, 
X-rays and neutrons by themselves exert no biologic effects. 
The changes are produced entirely by virtue of the charged 
particles which these radiations produce as secondary pro- 
ducts. These secondary products in turn, directly or ind- 
directly, produce ionization within the tissues. Nuclear rad- 
iations. produce no .effects on living tissue other than those 
produced by fast charged particles. 
Neutrons produce charged particles as secondaries in 
living tissue and these in turn produce highly destructive 
dense local ionization, often referred to as ion- 
ization”. 
X-rays and gamma radiation both produce light char- 
ged particles (electrons) as secondaries in living tissue. 
These cause ionization which is far less dense. On the 
other hand they are biologically very active as they cover 
a much greater volume than that caused by the heavy 
charged particles. 
ETIOLOGICAL CONSIDERATIONS IN CONNECTION WITH 
THE PATHOLOGICAL CHANGES PRODUCED BY ION- 
IZING RADIATION 
Under the microscope, tissues which have been damaged 
by radiation appear the same qualitatively regardless of 
whether the damage was induced in them by therapeutic 
irradiation with X-ray, over-exposure to radium, exposure 
to the ionizing radiations of an atomic bomb, or as a re- 
sult of bombardment with the neutrons from a cyclotron. 
This tissue response is the same qualitatively no matter 
which the form of radiation as long as it is penetrating 
external radiation; 
In the intensity of the injury received, and quantita- 
tively as far as depth and extent of injury is concerned, 
the changes may vary materially. 
114 If the dosage of the exposure is great enough to have 
biologic effect, this is produced through the formation of 
ion pairs as a consequence of their effect on the protoplasm 
of the cells involved . It is likely that the processes of 
normal cellular metabolism are interferred with through 
the disruption of enzyme systems essential to the normal 
living of tissue. Cells may be killed or simply injured by 
ionizing radiation. 
Genetic Effects 
It has been known since the early days of X-ray that- 
ionizing radiation can produce sterilization; sterilization on 
a large scale was seen after the atomic blasting of Japan. 
SUll, many wild and fantastic rumors are current and there 
is considerable popular confusion as to what is meant by 
sterilization and impotency. A vast amount is still to be 
learned about genetic effects on human beings and a long 
time will be required* before the answers are in. Neverthe- 
less a few statements can be made to clarify the matter. 
Ionizing radiation can produce sterility as a primary 
effect but not impotence. Impotence, when it occurs in 
connection with radiation is a by-product of the various 
debilitating effects of severe radiation illness. Sterility is 
often temporary. Pregnant women who were victims of 
heavy dosage in Japan did not bear monsters. Abortions 
and miscarriages were the results. 
In regard to future generations, geneticists point 
out the following: 
(a) Ionizing radiation in sufficient dosage can cause 
an increase in mutations, largely recessive. It further 
appears that all dosage is cumulative in this respect. 
(b) Most mutations are detrimental and will often 
result in obscure physiological weaknesses rather than 
spectacular or bizarre malformations. 
(c) The human race already appears to have a con- 
siderable number of unfavorable mutations and it is unwise 
to add to the number. 
The practical conclusions we can draw from these 
considerations are: 
(a) It is extremely important to adhere religiously 
to the standard scale of maximum permissible dosages or 
tolerances and in addition to avoid all unnecessary exposure. 
115 (b) It is however, also important to avoid the 
other extreme of envisioning all manner of dire effects 
from the controlled exposures of clinical radiology or in 
connection with work involving properly controlled radia- 
tion hazards. 
General Consideration of Cellular Pathology 
The cellular changes which are observed in tissues 
injured by radiation are not in themselves pathognomonic 
of radiation injury. As a matter of fact there may be 
close similarity between the cellular changes produced in 
tissue by radiation to those produced by other forms of 
trauma, such as thermal burns, chemical poisons, infec- 
tions, and extremes of malnutrition. Quite naturally tissues 
vary in their response to insult by these various agents. 
No single agent other than radiation, however, produces 
the same type of injury in the same diversity of tissues 
in the same individual. The changes produced in like 
tissues of different individuals may be so alike as to be 
indistinguishable and yet the injurious agents quite differ- 
ent, In this respect the testes of the males at Hiroshima 
often provided interesting changes in the reproductive cells. 
However, similar changes were found in the testes of many 
prisoners of war of both American and Japanese as a Je- 
suit of malnutrition. Furthermore, the bone marrow of a 
patient dying from benzol poisoning, or from agranulocy- 
tosis, may be in itself quite indistinguishable pathologically 
from the bone marrow of a fatal case of radiation sick- 
ness. It would be unwise to make a pathological diagnosis 
of radiation injury based solely on the findings of a single 
organ, or on the clinical laboratory findings based on the 
failure (or response) of a single organ. Caution must 
therefore be exercised in evaluating the etiologic implica- 
tions involved in a consideration of the changes observed 
in similar tissues, or organs, of different individuals. 
For purposes of this manual, it is not considered 
necessary or advisable to go further into a discussion of 
the gross or microscopic pathology. Since the tissue 
charges are no different from those produced by penetra- 
ting X-rays, the reader is referred to the various publica- 
tions on the pathological effects of X-rays and radium if 
more detailed information on the subject is desired. It 
might be of interest to note here that, prior to the atomic 
explosions in Japan, autopsies were not conducted in that 
country as a general rule. Many of the victims of the 
bomb were subjected to a careful post mortem examina- 
tion, however, and a quantity of material was made avail- 
able for study after the surrender. Several very interest- 
ing papers are now in the process of preparation and will 
shortly be available. Clinical Features and Clinico - Pathologic 
Findings 
It is relatively simple to visualize the clinical find- 
ings and clinical course which is characteristic of radiation 
sickness on the basis of the sensivity of the cells and or- 
gans involved and their reaction to this form of injury. The 
remarks which follow present the outstanding features as 
they were observed subsequent to the air burst in Japan. 
They are essentially what the expert Radiologist would have 
anticipated. 
Severe Exposures: Earliest Deaths 
In the most severe cases, death may occur within a few 
hours. Severe weakness and prostration, a state of extreme 
shock ana a dulled sensorium with little else in the way of 
clinical or pathological findings is characteristic of this 
group. There may be fever. The exact mechanism of in- 
jury and death in this type of case is not understood. The 
clinical picture, however, is clear cut, and the prognosis 
completely bad. This type of severe exposure had rarely 
been seen in the human prior to the Hiroshima incident. 
In an attempt to rationalize possible thereapy, there has 
been much speculation as to the underlying abnormalities of 
the physiologic processes. Some investigators believe that 
the mechanism of injury is interference with cellular respira- 
tion, or to the wide scale disruption of the enzyme systems 
which are concerned with the metabolism of the nucleii of 
cells and, in particular, with the metabolism of nucleic acid. 
Other suggest that in the earliest deaths, the same mechan- 
ism may be involved which some believe to account for the 
severe and early states of shock encountered after exten- 
sive skin burns and after severe exposure to liquid must- 
ard gas or Lewisite. In the latter instance, it may be that 
the cholinesterase enzyme is disrupted. Still others feel 
that there may be specific injury to the sympathetic or 
autonomic nervous system as a result of physical injury 
(radiation) or toxic injury (protein break-down products). 
There is some evidence to suggest that severe exposures 
to mustard gas produces similar toxic effects. Still others 
believe that the mechanism-of shock here, as in other in- 
stances, is due to the intoxication of vital cells of the body 
as a result of the circulation throughout the body of the 
breakdown! products of protein from cells injured by ir- 
radiation. The role of injury to the adrenal is not clearly 
understood as correlation of the pathologic findings with 
clinical expression is not clear cut. Some investigators 
believe this to be very important in the early deaths. 
117 Severe Exposures: Death During the 
First Week 
Individuals severely exposed but not as severely so as 
those just described, are likely to present varying degrees 
of shock, even within a few hours of the incident. Anor- 
exia, nausea and vomitting, fever, and weakness and pros- 
tration may be the outstanding findings on the first day. 
There may be no evidence of skin injury. Pain and suffer- 
ing are likely to be absent unless there is concomitent ill- 
ness or injury. The sensorium is dulled and the individual 
is more likely to be apathetic than agitated. Death may 
occur on the second or third day. Blood counts taken a 
few hours after exposure may reveal a decrease in total 
leukocyte count and this decrease will invariably be noted 
on the second day. Before death, the count may drop to 
500 or below. There may be a bothersome diarrhea be- 
ginning on the second day, rarely before. This will be- 
come progressive if the individual survives beyond this 
time. The diarrhea will be watery early but will tend to 
become bloody. Late in the first week, secondary infection 
and a tendency to spontaneous bleeding will become serious 
complications. Severe angina is not uncommon at this time 
There njay be ulceration of the tonsils, of the mucosa of 
the large intestine and, of the labia in women. 
In general, the earlier the appearance of systemic re- 
action, the more grave the prognosis. The same is true of 
an early depression of the leukocyte count. Complications 
are of utmost importance but difficult to evaluate. 
Severe Exposures: Death After the First Week 
In individuals who survive the first week, the initial 
symptoms are not likely to be so severe or as early in 
their appearance. White blood counts will reveal an early 
supression of lymphocytes followed by a decrease in the 
granulocytes. The accompanying grapns (fig. ) indicate 
the approximate results of the differential count. The total 
white blood count may fall to less than 500. After the 
third or fourth day, a tendency to bleed may be an outstand- 
ing feature and may be an important factor in determining the 
outcome. Hemorrhage may occur into lany organ or from any 
membrane. Bleeding from the mouth and gums, intenstinal 
bleeding, and hematuria are to be expecte. There may be 
petechial hemorrhages into or under the skin, into the retina, 
the myocardium, or the cerebral tissues. This hemorrhagic 
tendency is associated with (a) a reduced number of plate- 
lets, Cb) possible some humoral disturbance involving an anti- 
anti-hist amine like substance, and (c) increased capillary 
permeability. The reduction of platelets and increased 
118 capillary permeability can be observed objectively. 
During the latter part of the first week and there- 
after, various forms of secondary bacterial invaders may 
complicate the picture. Due to the supression of the lym- 
phocytes and granulocytes and to the destruction of lym- 
phoid tissue, there is a markedly decreased or completely 
absent resistence to infection. This may result in inva- 
sion of the intestinal mucosa by the normal intestinal flora, 
in bacteremia, boils and carbuncles, ulceration of the ton- 
sillar areas and angina with marked necrosis of the lary- 
ngeal tissue. Such lesions may reveal no lymphocytic in- 
filtration, only macrophage type of cells. In cases of 
thermal burns or other skin injuries, the secondary infec- 
tion seriously delays healing and promotes the formation of 
scar tissue. This may become luxuriant and unique in its 
characterisitcs. It resembles keloid and it is thought that 
this scar tissue may in the future become malignant. 
It may be of interest to note here that an occasional 
case with an apparently grave prognosis may evidence some 
response to bacterial invasion and produce an elevation of 
the white blood count. This would normally be considered 
a favorable sign since it would indicate that complete 
paralysis of the hematopoeitic function had not occured. 
In a patient who survives the first week, there is 
very likely to be a profound anemia which will be the re- 
sult of a combination of failure of the erythropoietic tissues 
and loss of blood. Both the red blood count and the hemo- 
globin will be reduced. In the more severe cases, .there 
appears to be a complete paralysis of all marrow function 
and the clinical course and blood picture are similar to 
those found in fatal benzol poisoning and other forms of 
‘ ‘panmyelophthisis’ ’. 
Ingestion Type of Radiation 
The symptomatology, prognosis, and treatment of the 
condition which results from the aspiration or ingestion of 
radioactive material are identical to those observed in the 
cases which resulted in the radium dial painters. Since 
these have been extensively mentioned and described in 
the medical literature, it is not considered necessary to 
review them here. 
119 RECOVERY AND CONVALESCENCE 
The more severe the illness, the longer recovery is 
likely to require. In the casualty and death producing 
ranges of exposure, there is little individual variation and 
husky persons are not more resistant to the radiation than 
the less robust. However, in cases of less intensive ex- 
posure where secondary infection, hemorrhagic tendency, 
etc., are so sommon as to be considered an integral part 
of the clinical picture, constitutional endowment, age, and 
some secondary external factors may be of great importance 
in determining the outcome of an individual case. Resis- 
tance to infection, local or generalized, is a variable factor 
and depends in part on the individual’s resistance and in 
part on the characteristics of the invading organism, the 
response to specific therapy, etc. 
Changes in the intestinal tract may seriously hamper 
the assimilation of food and produce severe states of mal- 
nutrition. The intractibility of the diarrhea may assume 
very serious importance. 
Generally speaking, no definite course of convalescence 
can be predicted. The more severe the combination of 
complicating factors, the more difficult and protracted the 
convalescence. Individuals who do not become ill during the 
first two weeks are not likely to become ill at all. Those 
who do become ill but are able to survive the sixth week 
are very likely to recover. The time element involved, 
however, and the theraputic difficulties which might be 
encountered, are impossible of prediction. 
The general behavior of the cellular elements of the 
blood stream is shown in the accompanying charts; (fig, ) 
Radiation Injury of the Hair Follicles and Skin 
An individual who has received enough general body 
radiation to produce erythema is quite certain to die of 
acute radiation sickness. The hair follicles, are much 
more sensitive to radiation than the skin and it is possible 
for epilation to be produced by smaller, non lethal doses. 
Hair will be lost over the area exposed to radiation and, 
as has been previously noted under “Geometry of Radiation” 
the loss of hair may be unilateral. Epilation may occur 
prior to death in cases of fatal exposure when death occurs 
late in the illness. 
120 Deaths in Relation To Time After 
Exposure 
In Japan, the peak of the death curve occurred dur- 
ing the third week and fell gradually until the sixth week. 
Those who survived the sixth week had a relatively good 
chance of recovery; most of the deaths subsequent to that 
time were caused by secondary infections and were attri- 
butable to the impossibility of asepsis and antisepsis under 
the conditions which existed. 
Over compensation of The Blood Cells 
During Convalescence 
Occasionally, patients who have survived the first 
week of illness will be found to present an elevated leu- 
kocyte count as well as an increase in the hemoglobin and 
the total red cell count. The white blood count may be 
15,000 to 25,000, the red blood count, 6 - 6.5 million, and 
the hemoglobin, 110 - 125% (Sahli). The elevated white 
blood count is not necessarily evidence of infection. In 
these cases, the Differential count is thought to be of t- 
most importance. A count of less than 0.5% reticulocytes 
indicates a poor prognosis and one of over 1.0%, supports 
a good prognosis. 
Overcompensation Not To Be confused With Chronic 
Exposures of Low Intensity 
The irradiation may cause either an increase or a 
decrease in the total count may be confusing. Severe acute 
exposures will cause a decrease; as recovery occurs this 
will be followed by an increase over the normal count. 
Low grade, chronic exposures produce an increase in the 
count unless the total accumulated dose is of such magni- 
tude as to depress the function of the bone marrow. A 
few cases of this type were found among individuals liv- 
ing within an area where there had been an accumulation 
of “fall out” of radioactive materials. This same type of 
repeated exposure to X-ray is thought to account for the 
fact that leukemia is ten times more common in radio- 
logists than in individuals not so exposed to radiation. 
121 TREATMENT 
Early treatment of survivors is likely to be impos- 
sible because of the difficulty of getting to the bomb vic- 
tims, the probable lack of functioning medical facility, and 
the lack of availability of trained personnel and of proper 
instruments and material. 
Measures to be applied in the field before the casualty 
is removed-lo. a. medical facility. CAid station, emergency 
hospital, etc.) 
(a) Do not needlessly expose rescue or aid party 
personnel to grave external radiation hazards. Do 
not attempt to remove patients to a “clean’’ area 
for treatment until decontamination has been accom- 
plished to a safe degree. 
(b) Protect against shock and administer simple 
life saving, measures to acute cases where such is 
indicated and the situation permits. 
(c) Transport to proper aid station or hospital as 
soon as possible. Do not attempt transfusions or in- 
travenous procedures forward of the aid station. 
Remember the dangers of infection. 
Measures to be Applied in The Aid Station 
(a) Continue to protect against shock. 
(b) Administer such life saving measures as may 
be indicated by good medical judgement and permitted 
by the situation. 
(c) Select for whole blood transfusion only those 
cases in which medical judgement would indicate that 
some benefit could be derived. In cases which have 
obviously received massive over-dosage, transfusion 
and heroic treatment is NOT indicated. Decisions 
will be difficult to make but, in case of an atomic 
disaster, it is most probable that trained. personnel 
and all material (including whole blood) will have to 
be ridgedly rationed, conserved, and expended only on 
122 those who have reasonable expectance of recovery. 
(d) If possible on the second day, select cases for 
further intensive care on the basis of white cell 
counts providing other hopeless findings are not over- 
riding. If a patient has a total count of less than 
2.000, he should not be further transfused. If over 
2.000, he should be selected not only for transfusion 
but for the best medical and nursing care that it is 
possible to provide. If, on*the third day, the count 
has increased to 5,000, the chances of recovery are 
good but if there has been a further decrease, the 
chances of recovery are nil and no further expendi- 
ture of critical supplies is warranted. Total white 
blood count, is then, a guide for prognosis at this 
stage and indicates those Individuals who should be 
selected for “all out” treatment and those for whom 
treatment would be wasted. 
General Considerations .Applicable Particularly. alter, the 
Second. Pay 
(a) Good nursing care, asepsis and antisepsis. 
(i) Hygiene of the mouth and skin. 
(ii) Avoidance of parenteral treatments if 
possible. 
Cb) Penicillin and sulfonamide medication, orally 
if possible. 
(c) Streptomycin in cases of B Coli invasion or 
bacteremia. 
(d) Whole blood transfusions as indicated by blood 
studies. 
(e) Folic Acid and Liver Extract to support the 
transfusions. 
(f) Possibly, the administration of blood coagulent$ 
Vitamin K preparations, Congo Red, etc. The use of 
these preparations in man has not been investigated 
but they may be found to be of some value. 
The following is the final paragraph of the “Report 
on The Medical Studies of The Effects of The Atomic 
Bomb” by Dr. Masao Tusuzuki, Professor of the Tokyo 
Imperial University and Chairman of the Medical Section 
of the Japanese National Research Council: 
123 “The most Important measures for the treatment 
of the atomic bomb radiation injuries is careful protection. 
All patients are affected more or less by the radioactivity, 
these must recover by their own vital power. In the cases 
in which the vital organs are damaged beyond their ability 
to recover, medical care at the present time cannot help. 
We may have some hope of recovery as long as any res- 
erve power is remaining because the radiation exposure 
has occurred only once. We must, therefore, avoid such 
treatment as whipping a tired horse hastily. In other 
words, we should not be over-confident in the ability of our 
medical care. Our aim shall always be a promotion of the 
natural healing powers.” 
SOME THOUGHTS ON DISASTER RELIEF 
Any organization planning to cope with an urban dis- 
aster will have many important factors to contend with. 
For example, the destruction will be of such a scale that 
no help from the city itself or its inhabitants can be expec 
ted. Evacuation of population amounting to hundreds of 
thousands must be planned for. There may be no pos- 
sibility of entering portions of the devastated area for re- 
scue work, fire fighting, etc. None of the existing protec- 
tive agencies of the involved city will be capable of func- 
tioning in view of our present types of building construc- 
tion. Only those hospitals in outlying districts could be 
used. Medical stores as presently distributed would be 
inaccessible or useless. 
In view of these factors, a nation-wide organization 
for meeting the impact of such a disaster is imperative. 
Such an organization should be non-military and should in- 
clude all of the nation-wide and state-wide organizations 
such as the United States Public Health Service, the 
American Medical Association, the American Red Cross, 
the State Police Forces, etc. The demoralization which 
would be attendant upon an atomic disaster would be of 
such proportions as to produce a policing problem which 
could be accomplished only by a great number of previously 
trained and organized personnel. Large bodies of troops 
such as the National Guard or other elements of the Armed 
Services would probably be employed elsewhere. 
Thinking along these lines, several other factors come 
to mind. Adequate provision must be made for the detec- 
tion and marking of potentially dangerous radioactive areas. 
For several weeks, the services of several thousand doc- 
tors would be required, assuming that anything more than 
rudimentary first aid is to be attempted. Thousands of 
pints of blood would have to be immediately available “on 
124 the job and judiciously used to insure the saving of lives 
which would otherwise be lost. The housing problem would 
be virtually insurmountable. 
In addition to the above general considerations, there 
are certain specific points which should be given careful 
consideration at this time. The matter of transportation 
and communication is of prime importance. Inter-city 
communication by rail and roads should be markedly im- 
proved with maximum avoidance of.congested areas. This 
is especially important in the case’ of roads. Divided 
traffic lanes are essential. The principle of dispersion 
should be applied as widely as possible. 
Provision should be made at or near the periphery of 
all large centers of population for adequate underground 
storage of essential supplies and equipment. This should 
include fire fighting apparatus, cranes, bulldozers, etc., 
with caterpillar treads, suitable gas masks, protective clo- 
thing, etc., as well as medical materiel. 
Extensive underground shelters having efficient air 
filtration systems and positive pressure maintenance should 
b§ provided. These would have to be numerous and scat- 
tered and should have food and water supplies and adequate 
sewage systems to provide for an extended occupancy by 
large numbers of people. 
125 
TNOWKi 0—48 -!> GLOSSARY 
and 
INDEX GLOSSARY. 
ABSOLUTE ZERO— The temperature at which there is a 
complete absence of heat. The temperature at which all 
molecular motion ceases. It is equal to -273° C or -460°F. 
ACTIVATION ENERGY — The amount of outside energy 
which must be added to a nucleus before a nuclear reaction 
will begin. 
ALPHA PARTICLES -- A helium atom minus its two orb- 
ital electrons. It is given off by certain radioactive sub- 
stances and has two fast charges. 
ALPHA RAYS — Streams of fast moving helium nuclei. 
ALTSBNATINQ--CUBHENT — (a.c.) - A current which 
periodically changes its direction of flow. 
ANODE — The positive electrode. The electrode to which 
negative ions are attracted. 
ATOM -- The smallest division of an element that can 
enter into a chemical change. 
ATOMIC NUMBER— The number of protons in the nucleus, 
hence the number of positive charges on the nucleus. Also 
the number of electrons outside the nucleus. The essential 
feature which determines the properties of an element and 
distinguishes it from all other elements. It determines 
the position of the element in the periodic table. 
ATOMIC WEIGHT -- The relative weight of an atom based 
upon oxygen with an atomic weight of 16. Numerically 
equal to the total number of protons and neutrons in the 
atom. 
AVQGAPRONS LAW — Equal volumes of gasses at the same 
pressure and temperature contain equal numbers of mole- 
cules. 
AVQGADRO*S NUMBER - The number of molecules in a 
gram molecular weight of a substance, i.e., 6 x 1033 mole- 
cules. 
BETA RAYS— Streams of electrons from radioactive sub- 
stances. 
BRITISH THERMAL. .UNIT — Cbtu) — That quantity of heat 
necessary to raise the temperature of one pound of water 
one degree Fahrenheit. 
CALORIE — The amount of heat necessary to raise the 
temperature of one gram of water one degree centigrade. 
CATHODE -- The negative electrode. The electrode to 
which positive ions are attracted. 
CENTRIPETAL FORCE -- The force which keeps a mov- 
ing body travelling in a circular path. The force is dir- 
ected toward the center of the circular path, 
CHANGE STATION -- A special compartment or building, 
set apart fro personnel decontamination. 
COULOMB A unit of electrical charge. The number of neg- 
ative electric charges carried past a point by a current of one 
ampere in one second. 
129 COULOMB S LAW — The force of repulsion between two 
like charges is equal to the product of the charges divided 
by the square of the distance between their centers. 
CRITICAL SIZE -- The minimum amount of a material 
which will support a chain reaction. 
CURIE— The quantity of radon in equilibrium with one 
gram of radium. 
DECAY TIME — (See HALF LIFE) 
DENSITY — The compactness of a substance, measured in 
terms of mass per unit volume. 
DEUTERIUM -- The heavy isotope of hydrogen having one 
proton and one neutron in the nucleus. Symbolically repre- 
sented as 
DEUTERQN -- The nucleus of a deuterium atom, containing 
one proton and one neutron. 
DIRECT CURRENT -- (d.c.) -- A current which always 
flows in the same direction. 
DYNE — A unit of force, which when acting upon a mass 
of one gram, will produce an acceleration of one centimeter 
per second per second. 
ELECTRODE — An electrical conductor inserted into a 
liquid, solution, or gas. 
ELECTROLYSIS -- The decomposing of a chemical com- 
pound by means of an electrical current. 
ELECTRON— A very small negatively charged particle, 
a component of the atom. 
ELECTRON VOLT — The kinetic energy an electron acq- 
uires when it is accelerated in an electric field 
by a potential difference of one volt. Equal to 1.6 x ICT 
ergs. 1,000,000 * 1.6 x 10“b ergs o* 0.0011 mass unit. 
ELECTROSC OPE — An instrument for detecting the pre- 
sence of electric charges by the repulsion of gold leaves. 
ELECTROSTATIC UNIT — (e.s.u.) — That quantity of 
charge which, when placed in a vacuum one centimeter dis- 
tance from a like equal charge, will repel it with a force 
of one dyne. 
ENDOTHERMIC -- A reaction which absorbs heat. 
ENERGY — The ability to do work. 
ERG— A unit of work equivalent to that done by a force 
of one dyne acting through a distance of one centimeter. 
A unit of energy which can exert a force of one dyne 
through a distance of one centimeter. 
EQUATION -- A symbolic representation used to indicate 
a chemical or nuclear reaction. The sum of the quantities 
on each side of the equality mark must be equal. 
FARADAY — The amount of electricity required to liber- 
ate from a solution one gram molecular weight of hydrogen 
ions or its equivalent. Equal to 96,500 coulombs. 
FILM BADGE -- A small piece of X-ray or similar photo- 
graphic film enclosed In a light-proof paper usually crossed 
by lead or cadmium strips. This is carried by the individual 
in a small metal or plastic frame called a film badge'holder. 
130 The badge is used to determine the amount of radiation which 
an individual receives. 
FISSION - The act of splitting or breaking apart of a nucleus. 
FREQUENCY - - The number of cycles of a wave motion com- 
pleted in a unit time. 
FUSION - The act of coalescing two or more nuclei. 
GAMMA RAYS - - High frequency electromagnetic radiation 
from radioactive elements not consisting of particles at all, 
hence undeflected by electric or magnetic fields. Similar in 
nature to X-rays, but having a higher frequency and more 
penetrating. The move with wave motion at the speed of light. 
GEIGER COUNTER — A device using an amplified discharge 
from a high voltage battery through an ionized gas to detect 
the presence of radiation 
GRAM MOLECULAR-WEIGHT. -- A mass in grams of a sub- 
stance numberically equal to its molecular weight. The weight 
in grams of 6.0 x molecules of a substance. A mole or 
gram mole. 
HALFLLIFE -- The time required for a given quantity of a 
radioactive element to decay so that only half of it remains. 
It is independent of temperature, pressure, presence of cat- 
alysts, amount, or other factors which influence chemical re- 
actions. 
HEAVY WATER -- Popular name for water which is composed 
of two atoms of heavy hydrogen (deuterium) and one atom of 
oxygen. 
ION --An atom or group of atoms bearing an electric charge 
either negative or positive. 
IONIZATION -- The dissociation of the molecules of a subst- 
ance into ions. 
ISOTOPES -- Two or more forms of the same element differ- 
ing slightly in atomic weight but having the same chemical 
properties. All isotopes of a given element have the same 
atomic number of nuclear charge. The nuclei of all isotopes 
of a given element have the same number of protons, differing 
only in the number of neutrons. 
JOULE -- A unit of work or energy equal to ten million ergs. 
KIL QWATT -H OUR— That quantity of energy equivalent to the 
expenditure of one kilowatt of power forone hour. Equal to 
1*141 horsepower-hours. 
KINETIC ENERGY -- The energy a body possesses by virtue 
of its motion. Equivalent to the amount of work which must 
be done to bring a moving body to rest. E 
o 
LAMBDA— A greek letter commonly used to designate wave 
length in radiation. 
MASS -- The quantity of matter in a body. It is indicated 
by the weight of the body, or by the amount of force re- 
quired. 
MEAN FREE PATH--The average distance which a molecule 
or ion moves before colliding with another molecule. 
131 METASTABLE — A comparatively stable state of an element 
which, upon the addition of a small activational energy, will 
spontaneously break down with the liberation of energy. 
MEV — Million electron volts. (See Electron Volt). 
MILLICURE -- A unit of radiation intensity equal to the number 
of alpha particles (3.7 x 10?) emitted by a milligram of radium 
in one second. A radiation intensity emanating from a radio- 
active source which decays such that 3.7 x 10' atoms per sec- 
ond. 
MOLE — (See GRAM MOLECULAR WEIGHT). 
MOLECULAR WEIGHT -- The sum of the atomic weights of 
all the constituent atoms in a given molecule. 
MOLECULE — The smallest particle of an element which re- 
tains the chemical and physical properties of that element. 
MOMENTUM — The quantity of motion possessed by a moving 
particle. Measured by the product of its mass and its velocity. 
MONITORING — Determination by use of Geiger counters or 
other devices of the amount of radiation coming from a given 
object or present in a certain area. 
NEUTRON — An elementary nuclear particle with a mass 
approximately the same as that of a hydrogen atom, but elec- 
trically neutral. A proton closely combined with an electron. 
NTTCT .EONS — A common name sometimes applied both to 
protons and neutrons. 
NUCLEUS — The heavy, positively charged, central part of 
an atom made up of protons and neutrons. 
PACKING FRACTION — The difference between the atomic 
weight and the mass number of an element, divided by the 
mass number and multiplied by ten thousand. It indicates 
nuclear stability. The smaller the packing fraction, the more 
stable the element 
PHOTOELECTRIC EFFECT -- The emission of electrons from 
a substance by the action of radiant energy being absorbed by 
the substance. 
PHOTOGRAPHIC DOSIMETRY-- The determination of the 
degree of exposure to radiation by means of photographic film. 
POSITRON — A particle having the same mass as an electron 
but having a unit positive charge. 
POTENTIAL PIEEERENQE — The work required to carry a 
unit positive charge from one point to another. Usually mea- 
sured in volts. 
POWER — The time rate of doing work. Work done divided 
by the time required to do the work. 
PRESSURE — The perpendicular component of force applied 
to a unit area. Total force divided by total area. 
PROTON — A positively charged particle which is a compon- 
ent of the atom. Its charge is equal to the negative charge of 
an electron, but its mass is 1845 times as great as that of an 
electron. 
RADIQACTIVITY — A process whereby certain elements 
undergo spontaneous atomic disintegration in which energy 
is liberated, generally resulting in the formation of new 
132 elements. The process is accompanied by the emission of 
one or more radiations, such as, alpha particles, beta rays, 
gamma rays, positrons, nutrinos, etc. 
REACTION — Any chemical or nuclear change. 
ROENTGEN — The unit of electromagnetic radiation which 
will produce one electrostatic unit of ions in a cubic centi- 
meter of “free air”. 
SPINTHARISC OPE — A device for showing fluorescence 
due to a radioactive source by the scintillations caused by 
the impact of the alpha particles thrown off by the radio- 
active source against a screen coated with zinc sulphide. 
STATISTICAL , PRQGRS.S — A process whereby the number 
of particles undergoing a particular reaction or change is 
proportional to the total number of such patricles present. 
SURFACE TENSION — That property of a liquid by virtue 
of which it acts as an elastic envelope, tending always to 
contract to the minimum area. That phenomenon in a liquid 
due to the molecular attractions, which produces a tension 
tending to reduce the liquid surface to a minimum. 
VAT.ENCE — That property of an element that is mea- 
sured by the number of atoms of hydrogen (or its equivalent) 
with which one atom of the element will combine. 
WAVE LENGTH— The distance on a wave between two 
consecutive points which are in phase. The distance be- 
tween successive crests of a wave. 
WORK— The product of the acting force and the distance 
through which it acts. 
IMPORTANT CONSTANTS USED IN THIS ARTICLE 
Constant and Symbol 
Yalue 
Velocity or tight, c 
Planck s Constant h 
Avogadro Number, N 
Electron Mass, M0 
Electron Charge, e 
Fahaday, F 
2.998X1010 cm. per sec. 
6.628X10—27 ergs per sec. 
6.023X1Q23 molecules per mol. 
9.1154X10—23 (rm. 
4.8029X10— 
96,514 coulomb per gram equiv. 
Disintegration of One Pound of U235 = 11,400,000 kw. hr. 
133 APPENDIX A 
Radiological Safety 
Regulations 
of the 
Bureau of Medicine and Surgery 
U. S. Navy Department APPENDIX A 
FOREWORD 
These regulations, established by the Bureau of 
Medicine and Surgery, are designed to meet the require- 
ments of the overall Radiological Safety Program of the 
Navy, particularly in connection with the utilization of 
atomic energy. 
The serious nature of radiological hazards calls for 
the most scrupulous observance of the rules in detail. By 
so doing, harmful effects to personnel will be avoided. 
137 2. RADIOLOGICAL HAZARDS 
2.1 The harmful effects of X-, gamma, and corpuscular 
or particulate radiations are considered to be due to their 
ionizing effect on living tissues, resulting in cell injury or 
death. It is beyond the scope of this publication to provi- 
an extensive discussion of the biological effects of ioniz- 
ing radiations. However, for the purpose of clarifying 
these safety regulations, a few of the known fundamental 
principles are briefly presented: All types of tissues are 
susceptible to this ionization effect, blood-forming tissues 
being most sensitive. Regardless of the type of radiation 
involved the result in the cell is apparently the same. The 
degree of injury depends primarily upon the quantity of 
radiation absorbed by the cells of the body. There are 
marked cumulative effects and, in addition, late changes. 
2.2 In the field of Radiological Safety, two types of 
hazards are recognized. 
2.21 External radiation is that type which attacks the body 
from without. The source of such radiation may be an 
X-ray machine, or any material which emits gamma rays. 
Neutrons may also be considered in this category and like- 
wise beta radiating substances may be sources of external 
radiation hazards at very short range, effecting superficial 
tissues of the body. 
2.22 Even though it may seldom occur that the whole body 
be subjected uniformly to external radiation, it is never- 
theless necessary, in the interest of safety, to assume 
that this always takes place, and to regard each exposure 
to external radiation as “total body irradiation”, rather 
than “limited body irradiation”. 
2.3 Internal radiation is that type of hazard which exists 
when radioactive materials enter the body by Ingestion, 
inhalation, or through the skin as by way of an open wound 
Materials which emit gamma, beta, and/or alpha particles, 
such as radium or plutonium and other heavy, untable ele- 
ments may be absorbed and deposited throughout the body. 
These act as poisons to injure or destroy blood-forming 
organs and other tissues. Various fission products, par - 
ticularly those with a long half-life, and those emitting 
beta particles also present an internal radiation hazard 
when they enter the body. Clinical findings of injury may 
be produced in a few days or weeks in severe cases, or 
may not appear for years in cases where smaller amounts 
of radioactive material have been absorbed. 
138 2.4 Obviously, under conditions of atomic warfare, and 
in connection with industrial atomic energy operations, it 
is possible for an individual to be exposed to both external 
and internal radiation hazards. 
3. IQLEBANCES. 
3.1 The tolerances herein are stablished for observances 
in all phases of work in the Atomic Energy Program of 
the Navy. In the event of atomic warfare, or of an atomic 
disaster, it may, however, be tactically necessary to ex- 
ceed moderately these tolerances in accordance with a pre- 
viously determined scale of calculated risks, to the end 
that extremely urgent operations may be conducted with the 
lease exposure to personnel. But for routine peacetime ex- 
posure the tolerances stated herein are in effect. 
3.2 Although the term “tolerance’’ is used in reference 
to dosage of radiation there is no proof that living tissues 
are actually tolerant of ionizing radiation, even in the 
minute amounts everywhere present as “background”. The 
term “maximum permissible exposure” is also in general 
use by many authorities and is probably the better of the 
two terms. Accordingly, the word “tolerance” will be 
used herein to mean ‘maximum permissible exposure” 
rather than “maximum saife exposure”. 
3.3 These tolerances do not represent limits within which 
there can be complete disregard of exposure. The ai m 
must always be to avoid all radiation to the greatest pos- 
sible extent. 
3.4 In the practical application of these tolerance levels 
such factors as efficiency of the Instruments, geometrical 
considerations, and calibrations must be taken into account. 
Otherwise great discrepancies are apt to occur. 
3.5 The following tolerance levels apply for work with 
radioactive objects and materials, or in all radioactive 
areas. 
3.51 External radiation. The tolerance level for total or 
limited body exposure is 0.1 rem (roentgen equivalent man) 
in any 24-hour period. The 0.1 rem represents the total 
additive exposure from the independent components of all 
ionizing radiations involved, including X-rays, gamma rays, 
neutrons, and beta rays. 
3.52 Internal radiation. No amount of plutonium or a 
similar alpha emitting element is ever considered tolerable 
If exposure, by any means, is unavoidable, the following 
139 rules may be applied. The maximum permissible level for 
plutonium in the atmosphere, or for other alpha emitting 
heavy unstable elements, is tentatively set at 5 x 
micrograms per cc of air (or 3 x 10“H microcuries per 
cc of air) for an eight hour working day, six days per 
week, for a one year period. The object is the prevention 
of the deposition of a total of more than one microgram of 
plutonium or a similar alpha emitting heavy unstable ele- 
ment in the body during a person’s lifetime. A total of 
one microgram of plutonium or a similar element deposited 
in the body is considered a lifetime tolerance. 
3.51.1 The maximum permissible level for air contamina- 
tion by the more hazardous beta-gamma emitting isotopes 
(such as Iodine, strontium, barium) is considered to be 
approximately 10“° microcuries per cc of air. The gen- 
eral rule is to evacuate an area when the air content ex- 
ceeds 10“' microcuries per cc of air, and to wear masks 
when the content exceeds 10“® microcuries per cc of air, 
of above mentioned type of Isotope. 
3.6 In addition to other requirements stated herein, 
safety regulations and tolerances to be observed by the 
Radiation Laboratory, San Francisco Naval Shipyard, have 
been adopted from regulations of the Atomic Energy Com- 
mission and are set forth ki Appendix A which is hereby 
made a part of these safety regulations for this purpose. 
3.7 In the clinical use of radioactive Isotopes, the safe- 
ty provisions of Appendix B will apply. 
3.8 Detailed regulations governing permissible radiation 
levels in food and water supplies will be published at a 
later date. Pending such instructions, no food or water 
known to be, or suspected of being radioactively contam- 
inated shall be consumed. 
4. PERSONNEL B&WJSSMEmS. 
4.1 It is necessary that the least possible number of 
persons required for efficient execution cf any given task 
in a radioactive area be employed with a view to minimiz- 
ing the exposure of each individual. However, in any rad- 
ioactive area a sufficient number of personnel must be em- 
ployed to assure that no individual shall be exposed to more 
than 0.1 rem per 24 hours. In the event of accidental ex- 
posure in excess of this amount it will be necessary for 
the individual to be absent from further exposure until suf- 
ficient time has elapsed to reduce the total exposure to the 
permissible amount. 
4.2 Personnel exposed to ionizing radiation hazards, no 
140 matter how minimal, over long periods of time, should be 
granted a continuous period of 30 days each year during 
which no exposure will be incurred. This period should 
coincide with vacation leave when possible. 
4.3 All persons other than military personnel and civil 
service employees who are permitted to board any radio- 
active vessel or to enter a radioactive area under naval 
cognizance shall be allowed to do so only after signing a 
statement that they have been warned as to the presence of 
radiological hazards. Compliance with all safety regula- 
tions shall be required of such individuals during their 
visit, including use of protective clothing, devices, and pro- 
cedures as indicated. 
5. MEDICAL EXAMINATIONS 
5.1 Pre-examinations. All personnel, both civilian and 
military, who enter radioactive areas, or who board a rad- 
ioactlvely contaminated vessel will be required to have a 
complete physical examination prior to commencing such 
duty. These examinations will be conducted when practic- 
able by Radiological Health Officers. The examination will 
include a complete blood count, a sedimentation rate, 
urinalysis, and chest X-ray. The X-ray of the chest may 
be made by any available technique including 35mm micro- 
film. A record of finger prints of all fingers will be mada 
Criteria for qualifications and special methods of recording 
will be in accordance with succeeding paragraphs. 
5.2 Physical Requirements. Because the work in radio- 
active areas may require a certain amount of physical en- 
durance and agility and involve the wearing of masks and 
cumbersome clothing as well as vigorous personal decon- 
tamination, it is believed that only personnel without gross 
physical defects should be employed. Those civil service 
personnel who would be classified as being able to perform 
arduous work under the routine Civil Service examination, 
or those service personnel who are fit for active duty may 
be considered qualified for this work as regards to their 
general condition. Personnel not so qualified, who services 
are’essential to an operation may be accepted upon 
approval ofthee Bureau of Medicine and Surgery. 
5.3 In addition to the general physical requirements of 
the preceding paragraph, the following findings are consid- 
ered disqualifying for work entailing possible exposure to 
ionizing radiation. 
7HO;m O—4H 10 
141 5.31 Sian and Integument: 
All open wounds, whether cuts, abrasions, ulcera- 
tions, or inflammations, until healed. 
All conditions in which there are open or raw sur- 
faces or external roughened areas in which for- 
eign body may be deposited or which the examin- 
er believes may be aggravated by irradiation. 
Excess longitudinal corrugation and brittleness of 
the nails. 
Atrophic skin conditions. 
Severe chronic blepharitis. 
5.32 Sy.esEars,, Nqsq, .and Throat; 
Any severe infection, acute or chronic, of the eyes, 
ears, nose, or throat. 
Markedly enlarged tonsils. 
Allergic conditions of the nose or nasal sinuses, if 
active under working conditions. 
5.33 Mouth: 
Pyorrhea, or extensive pocketing of gums. 
Severe dental caries. 
Severe gingivitis or stomatitis. 
Any open lesions. 
Pre-cancerous lesions, including leucoplakia. 
5.34 Bfisplratory-^ystam: 
Any acute or chronic infection. 
Acute exacerbations of respiratory allergies. 
5.35 CardiQvascuLar. and Blood.. Systems: 
Total white count below 4,000 or above 12,000. 
On cases where abnormal white cell count may 
be due to transient diseases or other conditions, 
re-examination should be made upon recovery). 
Persistently abnormal differential count. 
Total red blood count below 3'.5 million or above 
6.5 million. 
Sedimentation rate persistently above 15mm/hr 
(Cutler or Wintrobe). 
5.36 (jqhUot.Ujinajy-^yatsm: 
Any acute or chronic urinary tract disease. 
Any persistently abnormal urinalysis. 5.37 .General: 
Any pre-cancerous disease. 
Changes in finger prints, indicative of atrophy. 
538 X-Ray Findings: 
Evidence of active infectious process or of bron- 
chiectasis. 
Evidence of changes secondary to respiratory all- 
ergies. 
Evidence of intra-thoracic neoplasms. 
5.4 Recording of Examination. The results of these ex- 
aminations will be recorded as follows: the physical ex- 
amination on the NavMed Form Y, the laboratory data on 
the NavMed Form HF27, the chest X-ray report on the 
NavMed Form 57, the fingerprint record on the NavMed 
Form 57. Each fingerprint will be labelled. AR forms 
will be prepared in duplicate. A statement will be entered 
under “remarks” on each Form Y, giving the known total 
previous exposure to radiation and the type of work being 
performed. The original copies of all papers for each per- 
son examined will be firmly fastened together and will be 
forwarded to the Atomic Defense Division, Code 74, Bureau 
of Medicine and Surgery. The X-ray film will be retained 
at each activity and kept in a permanent file. The dupli- 
cate of each examination will likewise be securely fastened 
and filed at the local Radiological Health Headquarters. In 
the case of Army personnel attached to the activity, pre- 
pare and forward one additional copy of the completed ex- 
amination to the Atomic Defense Division, Code 74. Civil- 
ian personnel records will be handled as are those of Navy 
personnel. A statement that a special radiation examination 
was given as provided in this publication shall be entered 
in the corresponding person’s health record, with the date 
of the examination. An abstract of the examination will be 
entered in the special Radiation Abstract of the Health 
Record when these special sheets become available. These 
abstracts are to remain in each Health Record for the 
duration of service of all personnel involved. 
5.5 Follow-Up ,Examination. All personnel working in a 
radioactive area will have a monthly follow-up examination. 
Examiners will be alert for signs of chronic radiation sick- 
ness, as lack of vitality, loss of appetite, weight loss, 
cracking of the skin of fingers, and excessive longitudinal 
corrugation and brittleness of the fingernails. 
5.51 Complete blood counts and an erythrocyte sedimenta- 
tion rate will be made at thb time of the pre-examination 
and the monthly examination, and at such other times as 
the Radiological Health Officer may require. All blood 
143 samples should be obtained under similar technique and at 
the same time of day for each individual. By so doing, it 
is likely that the effects of physiological variation in the 
composition of the blood will be minimized. Since a var- 
iety of changes is possible in the blood picture after ex- 
posure to radiation, all bood counts will require, in addi- 
tion to very careful laboratory technique, interpretation by 
a Medical Officer who is a Radiological Health Officer or 
one who is experienced in such work. 
5.52 Individuals presenting persistently abnormal findings 
should be removed from all exposure to radiation, and be 
given an exhaustive study, preferably in a naval hospital. 
This should include bone marrow studies and alpha and 
beta counts on the urine, and chemical analysis of the 
urine for radioactive and toxic elements. Care must be 
observed in the evaluation of abnormal findings, and the 
general physical condition of the patient at the time of the 
examination must be considered. Transitory illness or 
ailments, or concommittant diseases, must be noted. Known 
over-exposures or cases of possible radiation sickness 
should always be transferred to a naval hospital for study. 
5.53 The follow-up examination will be complete, except 
as follows: The dental examination need not be repeated 
if all teeth are absent and the mouth is otherwise normal. 
If all teeth are normal on the first examination, follow- up 
dental examination may be omitted unless indicated. Other 
portions of the examination, as measurements, may, at the 
discretion ofthee Radiological Health Officer, be deleted. 
In all cases of deletion of a statement must be made on 
the appropriate line of the Form Y justifying the omission. 
5.54 The chest X-ray, and fingerprints shall be repeated 
at six-month intervals, and upon completion of the individ- 
ual’s duties in radiation work. In cases of radiation sick- 
ness, or known over-exposure, chest X-rays and finger- 
prints will be taken as indicated. 
5.55 Wherever possible, follow-up examinations should be 
made at six-month Intervals for a period up to five years, 
of all personnel whose duties have involved repeated ex- 
posure to radiological hazards. 
6. PHOTOGRAPHIC DOSIMETRY 
6.1 Film Badges. These badges shall be worn by all 
persons working with radioactive materials and by all those 
entering a radioactive area. They shall be preserved as a 
permanent record of each person s exposure. 
144 6.11 All procedures involved In photographic dosimetry 
shall be conducted only by qualified Medical Department 
personnel. 
6.2 The film badge will be worn in a badge holder or 
carrier, which will be securely pinned on the left breast 
of the outer garment. The badges will be issued before 
the individual leaves the “change stations”, and the wearer's 
name, the film badge number and the date and hour will be 
recorded. Orderly records will be kept and will be de- 
livered to the custody of the photographic dosimetry unit at 
the end of each working period. At the close of each cal- 
endar week in the case of regularly employed personnel, 
the films will be processed and readings taken by means 
of an approved type of densitometer. Individuals will be 
permitted to return to the radioactive area..only if .the.prer 
vlous exposure has Jbeen recorded, and was below the 
accepted tolerance limit of 0.1 rem per 24 hours. If above 
the tolerance, the individual shall not be permitted to re- 
turn to the radioactive area until time has elapsed so that 
his total exposure has again become 0.1 rem per 24 hours 
for the total number of days. 
6.21 Under conditions, where personnel may possibly be 
exposed to high levies of radiations, either continuously or 
intermittently, the film badge shall be changed and processed 
daily and the Bureau of Medicine and Surgery shall be kept 
closely informed. 
6.2 Personnel will not handle their film badges while at 
work, nor tamper with them in any way. 
6A In landing operations or if working in inclement 
weather where the film is likely to become wet, the badge 
should be carried in a water-tight container such as a 
thin rubber latex bag. 
6.5 The film itself will be the Eastman Type K Industrial 
(dental) packet, or similar type, with a range of sensitivity 
from 0.05 to 2.0 roentgen. Personnel who may be exposed 
to high levels of radiation where monitors cannot previously 
make a detailed survey of the area, as for example, 
divers, should wear badges containing both the Eastman 
Type K industrial film, and also the Eastman Type A in- 
dustrial film. The range of the Eastman Type A film is 
0.1 to 10.0 roentgen. 
6.6 The films will be covered with a thin lead cross, 
which serves to differentiate between the beta rays, which 
do not penetrate the lead, and gamma rays which go 
through the lead. Thus the area beneath the cross will 
145 read only gamma and the exposed corner sections will read, 
for the most paid, beta. 
6.7 A number of the films from each factory lot of film 
badges shall be exposed to a given amount of radiation 
from a known radioactive source. These films, which shall 
thus have been calibrated and will be marked on the packet 
as having been exposed, and shall be developed and read 
with each group of films worn. In this manner, differences 
in film density due to any difference in temperature, or 
processing solutions, or any exposure from an extraneous 
source can be reconciled. 
6.8 Supplies of film badges may be obtained upon request 
from the Bureau of Medicine and Surgery Projects Officer, 
Radiation Laboratory, San Francisco Naval Shipyard. The 
request should state the number of badges required per 
month as well as the number on hand, and should ordinar- 
ily be made for a three-months' supply. Films thus sup- 
plied will include some calibrated films, unless otherwise 
indicated. 
6.0 Densitometers used in photodosimetry shall be of an 
approved photo-electric type, and may be obtained by local 
purchase or through the usual channels of supply. Densi- 
tometers at present approved by the Bureau are: 
Weston Photographic Analyzer - Model! 877 
Ansco-Sweet Densitometer - (Navy designation 
PH614/U) 
7. PROTECTION OF PERSONNEL 
7.1 Clothing - Clothing used by personnel working in a 
radioactive area shall be provided by the Navy and shall 
be suitably marked for identification as Radiological 
Safety gear. This clothing shall include: 
A plastic or hard hat, or other head covering as 
appropriate. 
A suit of coveralls fastened to the neck, with si 
sleeves rolled down and openings of pockets sewed 
up. 
Underwear. 
Socks. 
Gloves; canvas type for manual labor, surgical or 
other rubber gloves for laboratory lwork. 
Stout shoes or rubber boots covered by disposable 
“booties". 
7.11 Shoes may be worn without “booties" in laboratory 
146 work if the condition of the floors permit. Tolerance levels 
for contaminated shoes are stated in Appendix B. 
7.1 Equipment - Personally owned tools and other equip- 
ment should not be permitted to be used in radioactive 
areas. All necessary tools shall be Navy issue and shall 
be provided upon leaving the “change station”. Tools used 
in radioactive areas shall be segregated and monitored as 
deemed necessary by the Radiological Safety Officer and 
the Radiological Health Officer. When such tools are con- 
taminated so that they emit a radiation level of 0.1 rep per 
24 hours, gamma plus beta, or are contaminated with an 
alpha emitting material, they shall be decontaminated. 
7.3 Masks. 
7.31 A mask which is especially designed for protection 
against the inhalation of radioactive material is not avail- 
able at the present time. For work in a radioactive area 
where adequate supply of oxygen is present and where there 
are no toxic fumes or gases, the following masks are auth- 
orized for use: 
Army Assault Mask with the M-ll cannlster. 
Navy Combat Mask, Mk-IV with B-2 cannister. 
7.32 The following respirators have been authorized for 
work on CROSSROADS ex-target vessels only: 
The Willson 750 Respirator with the L or D 
filter. 
Mine Safety Appliance Respirator, Catalog No. 
CR8751 with filter No. 2133. 
Mine Safety Appliance Respirator, Catalog No. 
CR9316 with filter No. 2133. 
Mine Safety Appliance Respirator, Catalog No. 
CR17060 with filter No. 2139. 
7.33 Test for oxygen deficiency and for toxic or explosive 
gases will be made before any closed compartment is 
entered. In areas where a deficiency of oxygen exists, or 
is suspected to exist, or where noxious gases are present, 
the following breathing apparatus shall be used: 
Rescue Breathing Apparatus, or Positive Pressure 
Breathing Mask wifi uncontaminated air or oxygen 
supply. 
If such equipment is used it is essential that personnel be 
carefully instructed as to its use and be familiar with the 
safety precautions pertaining thereto. 
147 7.34 When using the Army Assault Mask with the M-ll 
cannisteroor the Navy Mark IV Maqjc with the B-2 canni- 
ster, all used cannisters shall be marked with the user's 
name, serial number, time (in hours and minutes) used in 
a contaminated area, date used, and place of duty or name 
of ship in which used. These cannisters, when replaced, 
or when the wearer is no longer employed, shall be sealed 
and tagged with the above information and be forwarded to 
the Bureau of Medicine and Surgery Projects Officer, Radia- 
tion Laboratory, San Francisco Naval Shipyard, San Fran- 
cisco, California, where permanent storage will be provided, 
7.35 The Senior Radiological Safety Officer will, upon the 
advice of the Radiological Health Officer, require personnel 
to wear above-mentioned masks when indicated. It is not 
necessary to wear a protective mask while performing 
duties such as monitoring or inspecting under dust-free 
conditions in the open, or topside on a ship. However, the 
Army Assault Mask or the Navy Mark IV Mask with the 
appropriate cannisters shall be carried at all times while 
in radioactive are sis. If, in the case of CROSSROADS ex- 
target vessels, a full-face mask is not worn, goggles to 
cover the eyes win be worn under dusty conditions when 
so advised by the Radiological Health Officer. 
7.4 Personal Articles. No matches, lighters, cigarettes, 
or other smoking articles, nor chewing gum, chewing to- 
bacco, nor edible materials shaH be carried to work while 
in radioactive areas. Watches, jewelry, and other valuables 
will not be carried aboard a CROSSROADS target vessel 
or into a radioactive area, owing to the difficulty which 
would be experienced in decontaminating such articles 
7.5 The Chaage.-Ste.tlQs. 
7.51 To insure that the workers are adequately protected, 
a definite procedure for personnel decontamination must be 
developed and rigidly followed at every activity where a 
radiological hazard exists. A change station or decontam- 
ination station must be established for this purpose. In 
this station there will be provided a non-contaminated 
locker room where workers and others may remove their 
street clothing. They will then enter a * ‘clean” or uncon- 
taminated room where they will receive a complete outfit 
of clean work clothing. They will don their clothing in the 
“clean” room, stop at a check-in desk and receive film 
badges and other necessary equipment, and then proceed to 
work. 
148 7.52 Upon completion of work the canvas booties and 
gloves of all personnel will be placed in a suitable container 
as they leave the radioactive area or the gangway, for dis- 
posal by sinking at sea. After removal of the gloves the 
film badges will be returned to the check-in desk by each 
individual. The men then enter the contaminated side of 
the “change station”, where tools, masks, helmets, rubber 
boots and gloves are returned for monitoring and decontam- 
ination. The remainder of the work clothing will then be 
removed. 
7.53 Handwashing facilities, including brushes for scrubbing 
the nails, will be provided which are separate from the 
showers. After grease, dirt and contamination if present, 
are removed from the hands by repeated scrubbing with 
soap and water, the workers will proceed to the shower and 
was the body, repeatedly soaping and rinsing, paying par- 
ticular attention to the hair and scalp. They will then dry 
themselves in the shower room, and be completely monitored, 
with special attention being given to the hair, hands, and 
soles of feet. A suitable hand counter should be used for 
monitoring the hands. Showers will be repeated as 
necessary until all contamination has been removed from 
the body. 
7.54 Head facilities will be provided on both the clean and 
contaminated sides of the change station. It is not nec- 
essary for complete personnel decontamination to be car- 
ried out prior to using such facilities. The worker should 
remove his gloves, roll his sleeves to the elbow, and 
thoroughly scrub his forearms and hands before utilizing 
the head facilities. 
7.55 It is pointed out that after such a “change station” 
has been in use for a relatively short time, the shower 
drains, laundry, etc. may become increasingly contaminated. 
It is suggested that where appropriate, in order to avoid 
such contamination of the sewage system, that suitable 
arr augments be made to establish the “change station” and 
laundry aboard a barge or lighter. It is considered that 
in present operations, the waste water may be allowed to 
drain into the harbor from such a change station without 
hazard. A lighter so equipped would have the further ad- 
vantage in that it could be moored in the immediate 
vicinity of a contaminated vessel for greater convenience 
to personnel. 
149 8. GENERAL RABIQL.Qffl:CSAL.SAFSTY 
■EECIIILATIQm 
8.1 Monitoring 
8.11 Monitoring of radioactive areas is performed by 
specially trained personnel, known as Radiological Safety 
Monitors. Results of such monitoring operations are re- 
ported to the Senior Radiological Safety Officer, who, with 
the .advice of the Radiological Health Officer, establishes 
working times in various areas. The length of time is 
determined during which the individual may remain exposed 
to the radiation in a given area so that he will receive no 
more than the tolerance level of 0.1 rem per day. 
8.12 Prior to entering each radioactive area, or boarding 
each radioactive vessel, permission must be obtained from 
the Senior Radiological Safety Officer. An official log will 
be maintained by the Senior Radiological Safety Officer 
containing the names of personnel entering the radioactive 
area, time of entrance and departure, and authority 
panting permission to enter. The name of the individual 
in charge of the boarding or working party will also be 
recorded in the Radiological Safety Log, prior to boarding. 
8.13 The Commanding Officer upon advice of the Radio- 
logical Health Officer, may make such distribution of avail- 
able radiological Monitors as will enable the requirement 
to be fulfilled that no person at any time be exposed to 
radiation of a level greater than 0.1 rem per 24 hours. 
In this connection it must be borne in mind, that whereas 
most radiation hazards will decrease as time goes by, the 
internal or toxic hazard from alpha emitters and from 
long-half-life fission products remains essentially unchang- 
ed. 
8.14 After a radioactive area has been monitored, some 
form of visual marking should be employed to indicate 
particularly active spots. Lanes should be mapped out 
through the less active areas. The lanes shall be mon- 
itored frequently and changed if radiological conditions 
warrant. 
8.15 Ultimate responsibility for safety of personnel rests 
with the Commanding Officer, and he will be advised by 
the Radiological Health Officer as to the situation. If the 
Radiological Health Officer believes the health of the in- 
volved personnel is being risked, he win promptly report 
such an opinion to the Bureau of Medicine and Surgery 
via the Commanding Officer of the Activity concerned. 
150 8,2 Safety Regulations for Work. 
8.21 Insofar as possible, access to a radioactive area 
should be limited to working personnel only. Sight-seeing 
and other non-essential activities should be discouraged. 
Measures shall be taken to prevent souvenir hunting and 
looting. Areas which have been found radioactive, and 
areas in which radioactive vessels are moored should be 
restricted to official business only. Sentries or guards 
should be posted to prevent access by unauthorized per- 
sons. 
8.22 Men will be warned to avoid stepping in pools of 
water since it is possible for “shifting ’ contamination to 
occur as fission products are washed by rain from one 
place to another. Likewise attention must be paid to avoid 
dust clouds and piles of rust, paint scale and other debris 
which may give rise to a dust hazard or be tracked about, 
as such material is apt to be highly contaminated. 
8.23 There must be absolutely no eating, drinking, smok- 
ing, or gum chewing while working in a radioactive area. 
Only when personnel have left the area and have been 
thoroughly •decontaminated may this be permitted. It may 
be necessary to prescribe such hours of duty that this 
regulation may be observed without undue hardship to per- 
sonnel. 
8.24 The head facilities on the contaminated side of the 
change station shall be monitored daily and decontaminated 
if me level of total radiation is more than 0,1 rep per 
24 hours, beta plus gamma, or when alpha contamination 
is present. 
8.25 It shall be the duty of the senior member of each 
working party to insure that no member thereof is allowed 
to work with any wound or open lesions on his hands. 
* 
8.26 All workers and inspectors shall be instructed that 
in the event of damage to his clothing, gloves or other 
protective equipment he shall leave the radioactive area, 
or vessel, immediately and return to the change station. 
8.27 Handling of objects must be kept to a minimum. 
Cotton gloves give some protection against contamination 
and injury of hands and should be worn at all times while 
at work. It must be remembered that distance is the 
best protection against external radiation. 
8.28 No clothing shall be removed or changed while in a 
radioactive area, or while on a radioactive ship. 
151 8.3 “Overhead” personnel, that Is, those whose duties 
are the care of a change station, laundry, or on any other 
assignment which requires contact with contaminat mater- 
ial shall be provided with film badges, monitored and de- 
contaminated just as if working in the radioactive area or 
vessel itself. The change station and laundry as well shall 
be routinely monitored, and decontaminated when necessary, 
proper records being kept of these procedures. 
8.4 Diving operations may be conducted as necessary. 
Prior to each descent, divers shall be processed through 
the change station like all other personnel. They will 
wear on their person film badges and pencil electrometer 
dosimeters. There must be no open wound on their body 
The air supply of the diving gear must be located so as 
to avoid the intake of air contaminated with radioactive 
dust. Upon surfacing, divers shall be monitored and re- 
quired to proceed through the change station in the usual 
manner. Their diving dress shall be monitored and de- 
contaminated if over 0.1 rep per 24 hours gamma plus 
beta. 
8.5 Contaminated work clothing which, after repeated 
laundering, reads over .005 rep per 24 hours, gamma plus 
beta, when monitored, shall be collected and disposed of 
by sinking at sea in deep water. All clothing contaminated 
by alpha emitting isotopes will be decontaminated until no 
alpha hazard is present. If after repeated laundering, any 
alpha emitter is present, clothing so contaminated will be 
also sunk at sea in suitable containers. 
8.51 Contaminated work clothing which reads over 0.1 rep 
beta-gamma/24 hours shall be laundered separately, as 
will all clothing contaminated with an alpha emitting sub- 
stance. 
8.6 Under no circumstances will contaminated clothing 
or other 'material be disposed of .by burning or burial. 
9. £QR- SALES .ALP 
MATERIAL,QDmAMLMAT£P PY ATOMIC 
BOMB TESTS. 
9.1 All radiological safety regulations in other sections 
of this publication shall be held to apply as well for work 
with vessels and material contaminated by atomic bomb 
tests. 
9.2 Radioactive vessels 
9.21 If possible, radioactive vessels should be moored in 
such locations that prevailing winds will not carry contain- 
152 inated dust, spray, or other materials toward any inhabited 
area or roadway. It must be carefully determined before 
each dust-producing operation is begun that no injury to 
persons nor contamination of property can result. 
9.22 Should it be desired t o dry dock the radioactive 
vessels, the utmost care must be taken in order that work- 
ing and other personnel be not exposed to excessive radia- 
tion nor that the dry dock itself be unnecessarily contam- 
inated. Contaminated debris must be carefully collected 
and disposed of during such operations. Sand blasting must 
be done by the wet method. Contaminated sand and debris 
shall be collected and dumped at sea. 
9.23 Ships' ventilation systems are not to be operated 
except as approved by Senior Radiological Safety Officer 
and Radiological Health Officer jointly, nor will portable 
blowers be used without such clearance. Extreme care 
must be taken in handling compressed air lines to avoid 
spreading contaminated dust by the air stream from a leak- 
ing or parted line. Dust samples using the “filter queen” 
or other suitable sampling device should be taken in a 
number of areas throughout the ship prior to extensive 
operations. Careful interpretation of this hazard will be 
made by the Radiological Health Officer on the basis of all 
information available. 
9.24 Since a fire in a radioactive vessel would be fraught 
with serious consequences, every precaution wiH be taken 
to prevent fire. Cutting, burning and welding should be 
kept to a minimum and then done only be properly pro- 
tected, qualified personnel when adequate fire fighting 
equipment is immediately at hand. Adjacent spaces should 
be examined to make sure that inflammable materials are 
not stored against the other side of bulkheads subjected 
to heat. 
9.25 If cutting, buring, or welding must be performed, 
the Radiological Health Officer will survey the situation 
and make recommendations to the Senior Radiological 
Safety Officer as to need for special ventialtion apparatus, 
type of mask to be used, and other necessary precautions. 
9.26 Dry sweeping of a radioactive space wiH not be done. 
This will not apply to small localized operations for 
collecting dust samples for analysis. If it is necessary 
to clean a space this can be done by swabbing or perhaps 
flushing down. Swabs will not be wrung out by hand but 
may be hung on the life lines to dry. 
9.27 The use of the rotary wire brush is specificaHy 
forbidden as being too dangerous in all respects. 
153 9.28 Working parties will make certain, prior to leaving 
the target vessel, that no one is left aboard locked in a 
compartment. 
9.3 Ship Clearance. 
9.31 The term “target vessel” is defined as a vessel 
exposed to an atomic bomb test. The policies governing 
decontamination and clearance of target vessels are estab- 
lished by high authority. 
9.32 Clearance of non-target vessels which have become 
contaminated during work on, or study of, target vessels, 
may be accomplished as provided herein. 
9.32.1 Operational Clearance, which permits a vessel to 
operate in the Western Sea Frontier is granted by the 
Commander of that Sea Frontier. 
9.32.2 Final Clearance is granted by the Bureau of Ships 
and the Bureau of Medicine and Surgery jointly, upon com- 
pletion of decontamination and monitoring in accordance 
with safety criteria established for that purpose by the 
Bureau of Medicine and Surgery. 
9.32.3 After a vessel has been granted final clearance there 
is no further restriction as to her operations, unless she 
subsequently becomes re-contaminated. In that event, final 
clearance is automatically revoked and the procedure for 
clearance must be carried out anew. 
9.4 Dry docks in which work has been done on contamina- 
ted ships shall be frequently monitored. The tolerance 
limit for areas, fittings and equipment of the drydock is 
established at 0.005 rep per 24 hours, gamma plus beta. 
There must be no alpha radiation, as detected by suitable 
low level alpha meters or alpha sensitive film. Areas and 
materials reading in excess of this level shall be decon- 
taminated. 
9.41 Upon completion of all work on radioactive vessels, 
and upon decontamination and final monitoring, clearance 
for the drydock may be granted jointly by the Bureau of 
Ships, the Bureau of Yards and Docks, and the Bureau of 
Medicine and Surgery. For final clearance there shall be 
no alpha contamination and the beta plus gamma radiation 
shall not exceed 0.005 rep per 24 hours. 
9.5 Decontamination of other radioactively contaminated 
material is normally the responsibility of the cognizant 
Bureau. Final Clearance of such material after decontam- 
154 ination has been accomplished may be granted jointly by 
the responsible Bureau and the Bureau of Medicine and 
Surgery. 
9.51 Acids and other waste materials which have been 
used to decontaminate ships' salt water systems, or other 
equipment shall be placed in suitable containers and dumped 
at sea. Care will be taken to avoid spilling such waste 
solutions enroute. 
9.52 All machinery and equipment Including hand tools 
used in working on contaminated vessels and equipment 
shall be monitored and decontaminated if the radiation level 
is above .005 rep/24 hours, gamma plus beta, or If alpha 
contamination is present. If such materials cannot be ren- 
dered safe by decontamination, they will be properly safe- 
guarded or disposed of at sea as appropriate. 
9.53 All decontamination procedures shall be carried out 
under the supervision of a qualified Radiological Safety 
Officer, who shall be advised by the Radiological Health 
Officer. 
9.6 Removal of radioactively contaminated materials 
from atomic bomb target vessels for purposes other than 
those concerned TTdth technical study must be authorized 
by the Chief of Naval Operations. 
9.61 All articles removed from the target ships under 
proper authorization will be monitored in a clear non-con- 
taminated area. They will be Marked for identification 
and a record made of pertinent data. It Is necessary that 
a positive control be exercised ever all material or objects 
taken from the target vessels. Suitable “Radioactive 
Warning ” signs will be attached. Highly radioactive mat- 
erials so removed will be handled by the least possible 
number of persons and in such a manner as to produce the 
least exposure to radiation. 
9.62 If it is desired to ship any of these radioactive mat- 
erials, they must be packaged properly so as to avoid 
accidental exposure, to prevent fogging of film In shipment, 
and' to comply with all governmental and other regulations 
for shipment, as well as with the provisions of the follow- 
ing section (Sec. 10). 
9.7 Vehicles used for transporting radioactive material 
should also be carefully monitored; the use of wooden-bed 
trucks and ‘ passenger vehicles should be avoided. Truch 
155 beds, carts, and other carriers may be covered with a 
tarpaulin or canvas before receiving material from the 
target ships, or radioactive areas. These protective 
covers may be re-used until they become contaminated by 
alpha emitters, or have a level of 0.1 rep/24 hours, 
gamma plus beta, at which time they shall be disposed of 
by sinking at sea. 
9.71 Likewise, surfaces of small boats which may be used 
In connection with work on the target vessels should also 
be monitored and decontaminated as necessary. Final 
clearance of small boats may be granted by joint action of 
the Bureau of Ships and the Bureau of Medicine and Surgery 
10. STORAGE. HANDLING AND SHIPMENT OF 
RADIOACTIVE -MATERIAL 
10.1 Storage, handling, and shipment of radioactive mater- 
ial involves very serious and Insidious health hazards and 
must be subject to regulation so that personnel will not be 
exposed to (a) radiation In excess of the permissible daily 
dose or 0.1 r or the physical equivalent of 0.1 r per 24 
hours. (b): neutron radiation in excess of the physical 
equivalent of 0.02 r per 24 hours. In addition, appropriate 
measures must be taken to prevent toxicological and Inter- 
nal radiation hazards resulting from inhalation, ingestion or 
absorption (as through open lesions) of radioactive mater- 
ial. 
10.2 When shipping radioactive materials, public health 
hazards are involved and must be adequately cared for. 
Therefore the provisions of Docket No. 3666 - Interstate 
Commerce Commission “In the matter of regulations for 
Transportation of Explosives and other Dangerous Articles” 
in amendment of Section 233 of the Criminal Code (Trans- 
portation of Explosives Act), and Part II of the Interstate 
Commerce Act, shall apply for shipping of radioactive mat- 
erials. Docket No. 3666 is included in this publication as 
Appendix C. 
MISCELLANEOUS. RADIOLOGICAL .REPORTS 
REQUIRED BY THE BUREAU OF MEDICINE 
AND, SURGERY 
11.1 Radioactively Contaminated Ex-CROSSROADS Mater- 
ial - Reports on - In order that the Bureau of Medicine 
and Surgery may be kept adequately' informed as to the 
distribution of radioactive ex-CROSSROADS material which 
has taken place, it is required that all activities having 
custody of such material submit the following reports: 
156 (a) An inventory of al] items of ex-CROSSROADS 
material on hand which is known to be radio- 
active. This inventory shall indicate the de- 
cate the degree of beta and gamm and alpha 
activity of each item, together with the date 
of each reading. If alpha has not been mea- 
sured, state whethei or not contamination 
may be present. 
(b) An inventory of all items of ex-CROSSROADS 
material which is suspected of being radio- 
active. It is the opinion of this Bureau that 
all materials which originate from CROSS- 
ROADS target vessels should be considered to 
be radioactively contaminated until proven 
otherwise. 
(c) A report upon receipt of additional ex-CROSS- 
ROADS material. This report should contain, 
in addition to the information required in 
Report No. 1, a statement as to disposition 
made of packing material in which the object 
was shipped. In this connection is is pro- 
vided that radioactive ex-CROSSROADS mat- 
erial may be disposed of only by sinking at 
sea or by replacement aboard the target ves- 
sel. Burning or burial of radioactive mater- 
ial is not authorized. 
(d) A report of disposition of all items of ex- 
CROSSROADS material whether by transfer or 
otherwise. Regulations concerning shipment, 
handling and storage of radioactive materials 
are given in Section 10 of these regulations. 
This report shall likewise indicate the degree 
of radioactivity of each object and shall state 
the maimer of packing and shipment. The 
outside of each container shall be monitored 
and the reading included in the report. 
11.2 The Radiological Health Officer of each activity con- 
cerned shall submit the following regular reports via of- 
ficial channels to the Bureau of Medicine and Surgery: 
(a) A Weekly Inspection Report. - in letter form 
of all radiological safety arrangments includ- 
ing change station facilities. 
(b) A Monthly Photographic Dosimetry Report of 
all exposed personnel indicating' in columns 
names, rate, number of days employed to date, 
total time exposed to date, total gamma 
780898 ()—48 11 
157 received to date, total beta received to date. 
In the event that any individual has received 
an exposure in excess of 0.1 rem in any 24 
hour period the circumstances connected 
therewith shall be explained as a part of the 
same report. 
(c) A Monthly Roster of all medical personnel 
on duty with Radiological Health Section. 
12. FIRST. AID 
12.1 All wounds sustained in a radioactively contaminated 
area, regardless of their severity shall be treated immed- 
iately in such a manner as to prevent absorption of the 
radioactive material which has been deposited into .the 
wound. Generally this is best accomplished by stimulating 
mild bleeding by means of manual pressure or by placing 
a trouniquet above the wound. At the same time the wound 
must be washed with soap and copious amounts of clean 
water, which must be kept available for this purpose. The 
injured person shall then be evacuated to the change station 
or decontamination center where the Radiological Health 
Officer shall determine the appropriate disposition to be 
made in his case. The formalities of complete decontam- 
ination of the injured person shall not be permitted to in- 
terfere with urgently indicated medical or surgical treat- 
ment, but may be deferred until they can be carried out 
without jeopardizing his general welfare. 
12.11 It must be remembered that if the casualty is not 
decontaminated, his body may be covered with radioactive 
dust, grime, etc., and he as well as his clothing shall be 
kept segregated in the dispensary or hospital until decon- 
tamination has been carried out. AH attendants shall take 
precautions as described for handling radioactive material 
while caring for such an individual. 
13. SAFETY IKQQCTRINATIOH, 
13.1 In order that personnel working in a radioactive 
area may be properly informed as to the hazards and as 
to the safety measures to be observed, it is necessary 
that organized indoctrination be provided. It is particular- 
ly important that those in immediate charge of working 
parties be cognizant of their specific responsibilities in 
regard to the supervision over and execution of safety mea- 
sures. 
13.2 It is recognized that personnel working under these 
exacting safety precautions may in time go “stale”. In 
order to provide a means for general discussion as well 
158 as for briefing and familiarization in hazards and safety- 
procedures and to keep all hands up-to-date in these res- 
pects, it is suggested that a regular meeting be held. It 
is felt that such meeting will be genuinely helpful to mor- 
ale. By this and other means responsible authorities shall 
disseminate such Information as is required to insure that 
all personnel concerned are thoroughly familiar with all 
safety precautions. 
13.2 Appropriate local Radiological Safety Regulations shall 
be prepared based upon the requirements herein by each 
activity engaging in operations which involve possible rad- 
iological hazards to its personnel or to the public. Fam- 
iliarity with these local regulations shall be required of all 
persons concerned. A copy of the Radiological Safety Reg- 
ulations of each activity shall be forwarded to the Bureau 
of Medicine and Surgery, Code 74, and to the cognizant 
Bureau for approval. 
159 APPENDIX B 
Excerpts from 
Interstate Commerce Commis- 
sion Regulations 
Regarding 
Transportation and Shipment 
of Radioactive Materials APPENDIX B 
The following are some pertinent exerpts from the 
rules and regulations of the Interstate Commerce Commis- 
sion regarding the transportation and shipment of radio- 
active materials: 
(a) “Radioactive material is any material or combina- 
tion of materials that spontaneously emits ionizing 
radiation. For the purpose of these regulations 
radioactive materials are divided into three groups 
according to the type of rays emitted at any time 
during transportation, as follows: 
(1) GROUP I - Radioactive materials that 
emit gamma rays only or both gamma and electri- 
cally charged corpuscular rays. 
(2) GROUP n - Radioactive materials that 
emit neutrons and either or both the types of rad- 
iation characteristic of Group I materials. 
(3) GROUP UI - Radioactive materials that 
emit electrically charged corpuscular rays only, 
i.e., alpha or beta, etc. 
Cb) Radioactive materials must not be offered for 
transportation via rail freight except as specifically 
provided in section 367, or except by special ar- 
rangements and under conditions approved by the 
Bureau of Explosives. 
(c) Not more than 2,000 millicuries of radium, 
polonium, or other members of the radium family 
of elements, and not more than that amount of any 
other radioactive substance which disintegrates at 
the rate of 100,000 million (10H) atoms per sec- 
ond may be packed in one outside container for 
shipment via rail express, except by special ar- 
rangements and under conditions approved by the 
Bureau of Explosives. 
NOTE: For purposes of these regulations one 
millicurie is that amount of any radioactive mater- 
ial which disintegrates at the rate of 37 million 
atoms per second/* 
(a) “Shipments of radioactive materials, made by 
the Atomic Energy Commission, or under its dir- 
ection or supervision, which are escorted by per- 
sonnel specially designated by the Atomic Energy 
Commission, are exempt from these regulations/’ (a) “Radioactive materials, are exempt from pre- 
scribed packing, marking and labeling requirements 
provided they fulfill all of the following conditions: 
(1) The package must be such that there can 
be no leakage of radioactive material under condi- 
tions normally incident to transportation. 
(2) The package must contain not more than 
0.1 millicuries of radium, or polonium, or that 
amount of strontium 89, strontium 90, or barium 
140 which disintegrates at a rate of more than 5 
million atoms per second; or that amount of any 
other radioactive substance which disintegrates at 
a rate of more than 50 million atoms per second. 
(3) The package must be such that no signi- 
ficant alpha, beta or neutron radiation is emitted 
from the exterior of the package and the gamma 
radiation at any surface of the package must be 
less than 10 milliroentgens for 24 hours. 
(b) Manufactured articles other than liquids such as 
instrument or clock dials of which radioactive mat- 
erials are a component part, and luminous com- 
pounds, when securely packed in strong outside con- 
tainers are exempt from specification packing, 
marking, and labeling requirements provided the 
gamma radiation at any surface of the package is 
less than 10 milliroentgens in 24 hours. 
(c) Radioactive materials such as ores, residues, 
etc., of low activity packed in strong tight contain- 
ers are exempt from specification packing and label- 
ing requirements for shipment in carload lots via 
rail freight provided the gamma radiation or equiv- 
alent will not exceed 10 milliroentgens per hour at 
a distance of 5 feet from any surface of the car. 
There must be no loose radioactive material in the 
car, and the shipment must be braced so as to pre- 
vent leakage or shift of lading under conditions 
normally incident to transportation. The car must 
be placarded by the shipper as prescribed in Sec- 
tion 541A and 552 of these regulations. Shipments 
must be loaded by consignor and unloaded by con- 
signee.’ ’ 
PACKING .AND SHIELDING 
(a) “Radioactive materials that present special 
hazards due to their tendency to remain fixed in 
the human body for long periods of time (i.e., rad- 
ium, plutonium, and radioactive strontium, etc.) 
must, in addition to the packing hereinafter pre- 
scribed, be packed in inside metal containers spe- 
cification 2R, or other container approved by the 
Bureau of Explosives.” (b) “All radioactive materials must be so packed 
and shielded that the degree of fogging of undevel- 
oped film under conditions normally incident to 
transportation (24 hours at 15 feet from the pack- 
age) will not exceed that produced by 11.5 milll- 
roentgens of penetrating gamma rays of radium fil- 
tered by 1/2 inch of lead. 
(c) The design and preparation of the package must 
be such that there will be no significant radioactive 
surface contamination of any part of the container. 
(d) The smallest deminsion of any outside shipping 
container for radioactive materials must be not less 
than 4 inches. 
(e) All outside shipping containers must be of such 
design that the gamma radiation will not exceed 
200 milliroentgens per hour or equivalent at any 
point of readily accessible surface. Containers 
must be equipped with handles and protective de- 
vices when necessary in order to satisfy this re- 
quirement. 
(f) The outside shipping container for any radio - 
active material unless specifically exempt by sec- 
tion 367 must be a wooden box Spec. 15A or 15B, 
or a fiberboard box Spec. 12B, except that equally 
efficient containers may be used when approved by 
the Bureau of Explosives. 
(g) Radioactive materials Group I, liquid, solid, or 
gaseous, must be packed in suitable Inside contain- 
ers completely surrounded by a shield of lead or 
other suitable material of such thickness that at 
any time during transportation the gamma rhdiatlon 
at one meter (39.3 inches) from any point on the 
radioactive source will not exceed 10 milliroentgens 
per hour. The shield must be so designed that it 
will not open or break under conditions incident to 
transportation. The minimum shielding must be 
sufficient to prevent the escape of any primary cor- 
puscular radiation to the exterior of the outside 
shipping container. 
(h)(1) Radioactive materials Group EL, liquid, solid, or 
gaseous, must be packed in suitable inside contain- 
ers completely shielded so that any any time dur- 
ing transportation the radiation measured at right 
anglps to any point on the long axis of the shipping 
container will not exceed the following limits: 
165 (a) Gamma radiation of 10 mrhm. 
(b) Electrically charged corpuscular radia- 
tion which is the physical equivalent* of 10 
mrhm. of gamma radiation. 
(c) Neutron radiation which is the physical 
equivalent* of 2 mrhm. of gamma radiation. 
(d) If more than one of the types of radiation 
named in paragraphs (a), (b), and/or (c) is pre- 
sent the radiation of each type must be reduc- 
ed by shielding so that the total does not ex- 
ceed the equivalent of paragraphs (a), (b), or 
(c). 
(h)(2) The shielding must be designed so as to main- 
tain its efficiency under conditions normally inci- 
dent to transportation and must provide personnel 
protection against fast or slow neutrons and all 
other ionizing radiation originating in the radioact- 
ive materials or any part of the aggregate con- 
stituting the complete package. 
(i) Liquid radioactive materials Groups I, n, or III 
must, in addition, be packed in tight glass, earthen- 
ware, or other suitable Inside containers.' The in- 
side containers must be surrounded on all sides 
and within the shield by an absorbent material suf- 
ficient to absorb the entire liquid contents and of 
such nature that its efficiency will not be Impaired 
by chemical reaction with the contents. If the con- 
tainer is packed in a metal container specification 
2R, or other container approved by the Bureau of 
Explosives, the absorbent cushioning is not required, 
(]*) Radioactive materials Group m, liquid or solid, 
must be packed in suitable inside containers com- 
pletely wrapped and/or shielded with such material 
as will prevent the escape of primary corpuscular 
radiation to the exterior of the shipping container, 
and secondary radiation at the surface of the con- 
tainer must not exceed 10 milirqentgens per 24 
hours, at any time during transportation. 
NOTE: In determining compliance with require- 
ments of paragraphs e, g, h, and j measurements of 
radiation must be made with a Landsverk-Wollan 
Electrometer Model L-100 or equally efficient 
standardized meter. 
*NQTE - For purposes of these regulations the 
“physical equivalent’’ of a roentgen is that amount 
of radiation that would be absorbed in tissue to the 
extent of 83 ergs per gram. (mrhm. is an abbrev- 
iation for milliroentgens per hour at 1 meter (39.3 
inches)). Each outside container of radioactive material Group 
I or n, must be labeled with a properly executed label as 
shown below: 
Radioactive Materials Label 
(Red printing on white) 
HANDLE 
CAREFULLY 
RADIOACTIVE 
.MATERIAL GLASS D 
POISON Group I or II 
Rq person shall remain withL. 
daree 
eggarily.. 
Do not place undeveloped film within 
15 feet of this container. 
Principal radioactice content 
Activity of contents 
Radiation units from package No. 
Not more than 40 units shall be loaded in one car 
or one motor vehicle or held at one location. 
This is to certify that the contents of this package 
are properly described by name and are packed 
and marked and are in proper condition for 
transportation according to the Regulation1- 
prescribed by the Interstate Commerce 
Commission. 
Shipper*s name required 
hereon for shipments by 
EXPRESS 
167 Each outside container of radioactive material 
Group HI must unless exempt by section367, be labeled with 
a properly executed label as shown below: 
Radioactive Materials Label 
(Blue printing on white) 
7 HANDLE CAREFULLY 
Radioactive material emitting corpuscular 
RAYS ONLY V 
Name of contents 
CLASS D POISON 
This is to certify that the contents of 
this package are properly described / 
by name and are packed and marked/ 
and are in proper condition for 
transportation according to / 
the Regulations prescribe/ 
\by the Interstate Com- / 
\merce Commission / 
Group m 
Shipper's nam£ 
Nrequired here'' 
xm for sMpt 
\ments m/ 
\e^^r/ss 
168 APPENDIX C 
Excerpts and Abstracts From 
Control of Radioactivity 
Hazards 
Excerpts and Abstracts from CHEMICAL AND ENGINEERING 
NEWS American Chemical Society, Vol. 25, Page 1862, 30 
June 1947. 
Copyright 1947 by the American Chemical Society and re- 
printed by permission of the copyright owner. APPENDIX C 
Excerpts and Abstracts from 
CONTROL OF RADIOACTIVITY HAZARDS (1) 
William H. Sullivan, formerly, Clinton Laboratories 
Monsanto Chemical Co., Oak Ridge, Term., 
(Present Director Radiation Laboratory, 
San Francisco Naval Shipyard, 
San Francisco, Calif. ■) 
In connection with safety regulations it is of interest 
to note something of the control methods set up at the 
Clinton Laboratories, Oak Ridge, Term., as outlined by Dr. 
William H. Sullivan in the article listed above. 
“CONTROLS OF HAZARDS” 
♦Strict controls are exercised in a number of ways: 
“(a) Consultation on plans and specifications be- 
fore construction of plant facilities. 
Cb) Continuous monitoring of working conditions. 
(c) Continuous monitoring of individual exposure. 
(d) Education of personnel regarding hazards. 
(e) Education of personnel regarding safe tech- 
niques. 
Cf) Maintenance of adequate and clean records. 
(g) Maintenance of research facilities io check 
calculations and detect unknowns.” 
“ACTIVITY HAZARDS COMMITTEE” 
The health and health physics groups are aided by an 
“Activity Hazards” committee conformed of representatives 
of all activities concerned and functioning as.follows: 
* (1) Disemination of information and liaison be- 
tween central safety groups and various activities. 
*(2) Aid to medical group in supplying informa- 
tion and formulating policies. 
*(3) Preparation and modification of regulations. 
*(4) Review of problems. 
*£5) Investigation and review of accidents and in- 
juries. 
“FORMULATION OF RULES AND PROCEDURES” 
“Tolerances. The generaHy accepted tolerance level 
♦ Abstracts 
171 for total or limited body exposure is 0.1 rem for a 24- 
hour period. . In general, it is considered un- 
desirable to work in radiation fields of greater than one 
roentgen per hour, which gives an exposure time limit of 
6 times. 
“Radiation Monitoring. The instruments for radiation 
surveys and monitoring should always be maintained in 
first-class condition and accurately calibrated. Persons 
within an area restricted because of activity hazards should 
wear a film badge and, if available, pocket meters. Persons 
working in a pile building itself or with neutron sources 
should be provided with special neutron monitoring devices. 
“PROTECTIVE CLOTHING. 
“(1) Shoes. In general, attempts made to decon- 
taminate shoes have not been very successful. The per- 
centage of recovery is usually very small. 
(2) Contaminated personal clothing. Personal 
clothing found to be contaminated should be appropriately 
labeled for identification and sent to a special laundry for 
decontamination or disposal. Such clothing, if it cannot be 
satisfactorily decontaminated, should be destroyed or bur- 
ied in an isolated place. (See Navy RadSafe Regulations). 
(3) Gloves. Suitable gloves should be worn when- 
ever hand contamination is probable. . It is re- 
commended that rubber gloves be worn while handling open 
vessels containing more than 10 micrograms of plutonium, 
while handling equipment suspected of alpha contamination, 
and, preferably, while working with quantities of plutonium 
greater than 1 microgram. ” 
“Decontamination of clothing. ”. Clothing 
should be laundred in a special decontamination laundry 
and classified as follows: 
‘ ‘ (1) Low beta and gamma activity - garments show- 
ing less than 500 counts per minute. 
(2) Medium beta and gamma activity - garments 
having from 500 to 10,000 counts per minute. 
(3) High beta and gamma activity - garments 
showing greater than 10,000 counts per minute. 
(4) Alpha contamination - garments worn in areas 
where alpha emitters are handled. 
“For each class of contaminated clothing there is 
specified a particular sequence of washing operations. — 
“The most effective decontamination agent for highly 
contaminated clothes is cetric acid. A typical sequence of 
operations including the acid treatment is hot rinse, hot 
172 (1) Keep the fingernails cut short. 
(2) Survey and wash hands carefully at frequent 
intervals, and especially before eating, smoking or leaving 
work. 
C3) Refrain from smoking in the laboratory. 
(4) Wash gloves before removing them from the 
hands. 
“For persons working with plutonium or other alpha- 
emitters of similar hazard there are several additional 
rules: 
(1) No work with such alpha emitters in any 
chemical or physical form is ever to be done by -a person 
having a break in his skin below the wrist or with a band- 
age on his hand. 
(2) Hands are to be checked at frequent intervals 
but not less than twice dally for persons working in lab- 
oratories where plutonium is being handled. 
(3) Special care must be exercised when using 
organic solvents so that skin contact with alpha emitters in 
any form is avoided, since these solvents may make the 
skin more permeable to the penetration and absorption of 
radioactive materials. 
(4) Any persons receiving a puncture wound sus- 
pected of contamination should report to the physician as 
soon as possible after the accident. For immediate care 
of a minor wound it is recommended that the wounded area 
be put under running tap water within 15 seconds of the 
time of the accident, if possible, and a mild tourniquet 
action should be maintained some 3 inches above the wound, 
in such a way as to stimulate mild bleeding during the 
washing phase. Scrubbing of the wounded area with a 
soapy brush and a large volume of water should be contin- 
ued for at least 5 minutes. In case of major wounds, a 
physician should be called immediately and a trouniquet 
applied proximal to the wound to stop venous flow but not 
restrict arterial flow except in cases of severe hemorrhage. 
“In cases of alpha or beta contamination of the hands 
without injury, soap and water and a brush should first be 
used, and with vigor, to remove as much of the contamina- 
tion as possible before using stronger solution. A proced- 
ure for washing contaminated hands which has proved to be 
satisfactory is as follows: 
(1) Wash thoroughly for 2 or 3 minutes by the 
clock with a teaspoonful of a lanolin or corn meal cleaner, 
using a sufficient amount of tepid (not hot) water to main- 
tain a thin paste and rub the paste over the entire sur- 
face of the hands and fingers. Rinse off completely with 
water and repeat the process at least three times. 
173 
7.H(K{»K 0—48 Vi rinse, hot 3% citric acid wash, hot rinse, hot suds, hot 
rinse, hot 1.5% citric acid wash, hot rinse, rinse, rinse, 
cold rinse, cold rinse, starch. 
“After the clothes have been washed, each article 
should be counted with a thin-walled Geiger counter tube 
located approximately 4 inches behind the one foot square 
screen on which the clothes are placed for measurement. 
If a garment shows a counting rate of greater than 500 
counts per minute, it should be returned for rewashing. -- 
No detachable amount of alpha contamination 
is tolerable. 
“PROTECTIVE DEVICES. 
“Respirators, .Combat Masks, and Air Line Hoods. It 
is recommended that an approved respirator, combat mask, 
or air line hood be worn in any location where the concen- 
tration of air-borne alpha emitters may be greater than 3 
x 10"microcurie per cc. . 
“EQUIPMENT AND FIXTURES. 
“Hoods in which plutonium or other alpha-or beta- 
gamma emitters of comparable hazards are actively being 
handled should be provided with nonporous, inert floors such 
as glass, tile, or metal and should contain preferably a 
stainless steel tray to catch any material from possible 
spiHs. . Particular care should be taken to 
see that the moving parts of open centrifuges are main- 
tained free from contamination. . 
“EATING AND SMOKING RULES: 
“The preparation, storage, or consumption of food in 
a laboratory or operating room where active materials are 
handled should be forbidden. The use of milk bottles or 
other food containers for handling or storing chemicals 
should also be forbidden. Coveralls, laboratory coats, or 
other protective garments worn in restricted area (subject 
to contamination) should not be worn to a common eating 
place. Smoking should be controlled by the local area rules 
which vary widely. However, it is general practice that 
persons do not smoke while working in a laboratory where 
active materials are present. Furthermore, it is recomm- 
ended that each individual survey his hands carefuHy be- 
fore smoking. 
“CONTAMINATION OF PERSONS. 
“It is recommended that all persons working with 
radioactive materials foHow a number of simple rules: 
174 (2) If the above procedure is not enough to re- 
move all dirt and contamination, the hands should then be 
scrubbed for a period of at least 8 minutes, by the clock, 
using a liquid or cake soap, hand brush, and tepid water, 
being sure to brush the entire surface of the hands, espec- 
ially around the nails and between the fingers. Light pres- 
sure should be exerted on the brush - that is, not so hard 
that the bristles are bent out of shape. Eight minutes is 
usually a sufficient time to allow three complete changes of 
tepid water and soap. Each one of the three washings 
should be so thorough that the brush will cover all areas a 
minimum of four strokes. A convenient routine is to start 
by scrubbing one thumb, being sure to brush all surfaces, 
proceed to the space between the thumb and first (index) 
finger, and similarly to each finger and the webbs between 
the fingers. Attention should be given to the palm and back 
of the hand and finally additional scrubbing of the nails and 
cuticles before proceeding in an exact manner with the other 
hand. 
(3) Lanolin or hand creams containing lanolin may 
oe used after washing to soften the hands and prevent chap- 
ping. 
“In cases of contamination of the hands or body by 
beta-gamma emitters, particularly fission products, an ad- 
ditional satisfactory decontamination procedure consists of 
applying a special paste containing principally titanium 
dioxide. It should be used initially as the paste and thin- 
ned as required with tap water while working the paste 
over the contaminated areas. A minimum of 2 minutes of 
thorough application of this lather is recommended, espec- 
ially around the fingernails. The lather should be removed 
by thorough rinsing of the hands or body area with luke- 
warm tap water, and this operation should be followed by a 
thorough washing of the hands or body area with soap and 
water, using a hand brush for most effective removal of 
the titanium dioxide. 
“The pipetting of solution by mouth should be forbid- 
den in laboratories handling active materials. Glass blow- 
ing in laboratories containing active materials should be 
discouraged. Any person who knowingly swallows, inhales, 
or receives injections of a radioactive material, who may 
have been overexposed to radiation from any source, should 
report to a physician as soon as possible after the accid- 
ent. 
“CONTAMINATION OF AREAS. 
“In general practice, all areas in which radiation 
levels are greater than 12.5 mr. per hour should be either 
roped off and posted with appropriate signs to prevent per- 
175 sons from trespassing or, where the hazard is of a per- 
manent nature, permanent signs posted, barricades instal- 
led, and existing doors locked. . 
“Before experimental work involving especially 
hazardous levels of activity is undertaken, suitable pro- 
tective measures must be mutually agreed to by all per- 
sons concerned. 
“STORING AND HANDLING OF RADIOACTIVE MATERIALS, 
“Beta-gamma sources should be stored in closed 
containers with sufficient shielding so that the radiation 
level is less than 12.5 mr. per hour on contact. A much 
lower radiation level, preferably l.to 2 mr. per is 
desirable if practical. . 
“Any work with alpha-emitting materials susceptible 
to atmospheric distribution by dusting, spilling, vaporiza- 
tion, and effervescence of solutions, etc., should be done 
in a hood having an air flow rate of at least 50 linear 
feet per minute or preferably 100 linear feet per minute 
with the hood wide open. . 
“Small beta-gamma sources may frequently be hand- 
led in light long-handled carriers. In this way, one seeks 
to miximize the advantages obtainable with distance — i.e., 
the inverse square law. A convenient guide to the radia- 
tion intensity of a given gamma ray-emitting source at 
different distances is given in the following, table: 
MILLIEOENTGENS PER HOUR AT VARIOUS DISTANCES 
FROM A 10 MILLICURIE SOURCE 
10 Me. of ac- 
tivity Having a 
Gamma energy 
of 
Will Give 
Will Give 
Will Give 
at 5 
at 1 cm. 
at 1 Foot 
Feet 
Mr. per 
Mr. per 
Mr. per 
M.e.v. 
hour 
hour 
hour 
0.5 
29,000 
31 
1 
0.8 
46,000 
38 
2 
1.0 
56,000 
60 
2.5 
1.5 
76,000 
81 
3 
1.8 
78,000 
83 
3.1 
2.0 
93,000 
99 
4.1 
2.5 
104,000 
111 
4.3 
3.0 
117,000 
125 
4.8 
4.0 
140,000 
140 
5.8 
“The covered carrier is considered to be the safest 
176 and best device for such transfers, but it has the disadvan- 
tage of being too heavy for convenient carrying. ——, 
“The light uncovered carrier is quite satisfactory for 
many operations and is much easier to handle than the 
covered carrier. It consists of a 2-inch diameter cylinder- 
ical aluminum cup attached to the end of a 5 foot length 
of 3/8 inch diameter aluminum tubing. . 
“If the radiation levels for solid materials packed in 
irradiation cans or as slugs exceed those tolerable for man- 
ipulations in the open at a distance of 5 feet or so, shield- 
ed containers should be used. -. 
“The method of transferring liquid samples depends 
somewhat on the volume of solution handled. 
“The most satisfactory device for the transfer of 
large amounts of solution consists of a 5-liter stainless 
steel flask enclosed in 2 inches of lead. . 
“The transfer of small quantities of solution is acc- 
omplished in several ways. 
“(a) One end of a 2 to 3 foot length of nylon cord 
or waxed string is tied around the mouth of a clean bottle. 
The other end is attached to the notched or hooked end of 
a 3 to 8 foot length of aluminum tubing (called the “fish 
pole”). . 
“(b) For transferring “tracers” level solutions in 
ordinary glassware, various types of tongs have been dev- 
eloped for use. It is recommended strongly that such tran- 
sfers be made by using- an auxiliary container or tray to 
minimize possible contamination by spillage. 
“TRANSPORTATION OF ACTIVE MATERIALS. 
“No active material or equipment is transported into 
or out of the site area without written authorization of 
some responsible person in the organization. 
“All radioactive materials transported into or out of 
the laboratory should be surveyed by a responsible person. 
“DISPOSAL OF ACTIVE TRASH AND UNWANTED ACTIVE 
MATERIALS. 
“Trash containing radioactive materials may disposed 
of according to a number of procedures but an effective 
one, which is based on a considerable amount of exper- 
177 ience, is outlined as follows: 
“Two cans painted entirely red are provided at each 
desired located for trash which is contaminated. These 
cans, which are used one at a time, are monitored at 
sufficiently frequent intervals to prevent active materials 
from accumulating to such an extent that the radiation level 
is greater than 12.5 mr. per hour or is full, it must be 
picked up by a special crew which takes the material out 
for disposal in an isolated area designated for this purpose.” 
178 INDEX 
A Page 
Activation Energy for fission and fussion 26 
Air Blast 109 
Assembly and detonation of the bomb 83 
Atom, The 5 
B 
Bohr’s Model of the Atom 13 
C 
Calculation of risks in connection with radio- 
logical hazards 105 
Cells 56 
Centrifuge method 113 
Chemical reactions 6 
Clinical features and clinico-pathologic findings . 117 
Contamination 99 
Critical size 65 
D 
Deaths in relation to time after exposure .... 121 
Definition - Radiation Sickness 112 
Delayed neutrons 71 
Diffusion methods of separation 57 
Dosage of exposure and how employed in cal- 
culating risk 107 
E 
Effective ranges, and estimation of probable 
casualty production at time of atomic bomb 
explosion 100 
Effects of an atomic explosion 60 
Electromagnetic methods of separation 103 
Electrometers 112 
Ethiological Considerations 
Ethiological considerations in connection with 
pathiological changes produced by ionizing . . 
179 E Page 
radiation 114 
Equivalence of Mass and Energy 40 
Explosion: Theory and practice 78 
Extrinsic factors influencing radiation exposure . . 113 
F 
Fan Out 96 
Field instruments for detecting of ionizing radia- 
tion 101 
Film badges 104 
Fission and fussion 18 
G 
Geigpr counters 102 
General considerations of cellular pathology .... 116 
General considerations of applicable particularly 
after the second day 123 
Genetic effects 115 
Geometry of radiation 93 
Glossary 127 
H 
Hazard of explosion 88 
I 
Incidence 112 
Induced radioactivity 95 
Industrial problems 99 
Ingestion type of radiation 119 
Inside the nucleus 20 
Instruments 101 
Internal body radiation 109 
Internal radiation 90 
Interpolation of meter readings into maximum 
allowable working times 108 
Introduction 1 
Ionization chambers 103 
Ionization in living tissues 114 
Ionizing radiation 110 
Isotopes 18 
180 J . Page 
K 
Kinetic theory 2 
L 
Low grade hazard as in normal safety operations . 107 
M 
Mass changes in nuclear reations 41 
Medical aspects . .. 86 
Moderators . . 72 
N 
Non-continuity of matter 1 
Nuclear bombardment with neutrons 50 
Nuclear fission 47 
Nuclear transformation 34 
O 
Overcompensation not to be confused with chronic 
exposure of low intensity 121 
Over compensation of the blood cells during conval- 
escence 121 
P 
Packing fraction, The 44 
Plutonium - Hanford plant 44, 75 
Plutonium production - Hanford plant 64 
Power output from pile 74 
Protons, Electrons and Neutrons 10 
Predicting nuclear reations 43 
181 Q Page 
R 
Radiation sickness Ill 
Radiation injury of the hair follicles and skin . . . 120 
Radioactive decay 32 
Radium and radioactive disintegration 28 
Recovery and convalescence 120 
Reliability of RadSafe organizations 106 
S 
Severe exposure: Death after first week 118 
Severe exposure:- Death during first week 118 
Severe exposure: Earliest deaths 117 
Slow neutron reactions 68 
Solid blast 110 
Some thoughts on disaster relief 124 
Summary of the Uranium production problems ... 61 
T 
Table of Periodic arrangement of the elements . . 84 
Thermal effect 109 
Thermonuclear reactions 84 
Thermal diffusion methods 60 
Time after detonation 106 
Treatment 122 
U 
Uranium fission . . / 51 
V 
W 
Wilson Cloud chamber 35 
Work of the Manhattan District 55 
182 
I' U S GOVERNMENT PRINTING OFFICE : O—1948