UNIVERSITY OF CALIFORNIA
July 10, 1964

LAWRENCE RADIATION LABORATORY
Pp. O. BOX 808
LIVERMORE, CALIFORNIA

Dr. Donald Rea

Space Science Board

National Academy of Sciences
800 Welch Road - Suite 214
Palo Alto, California

Dear Dr. Rea:

This note is intended as a preliminary reply to Prof. Lederberg's letter of
June 29 regarding the analysis of the Martian surface. He has divided the
problem into three questions dealing with the detection of life, the deter-_
mination of its nature if present, and the properties of the environment

in which it is found. I will try to state briefly how neutron activation
analysis might be applied to these problems. Ina few weeks, I will sub-
mit a more detailed report suggesting how some of the specific experiments
discussed here might be performed.

1) Diagnosis of the Presence of Life. Neutron activation analysis is
almost certain to be useless for this purpose. Neutron analysis methods
‘can be used to detect the presence of many nuclear species (sometimes even
if they are present only in very minute quantities) but they cannot deter-
mine the detailed chemical combinations of the elements present. Sometimes,
certain conclusions can be drawn about the chemical composition of the
sample from the abundance ratios of the elements. However, in the case of
organic or living matter this is very unlikely. Unfortunately, the most
important elements in living matter (carbon, oxygen, nitroge: and hydrogen)
are relatively difficult to detect by nuclear methods. It is very improb-
able that a neutron activation analysis experiment could be performed with
sufficient accuracy to tell the difference between "living" and “inert”
organic matter. (I am not even certain whether significant dif:-renees in
gross composition exist between "inert" materials such as starcn and living
proteins. ) Thus, for the detection of living matter, sther methods will
have to be employed.

2) Nature of Life if Present. This question also is probably one for
which nuclear activation methods are inapplicable. The “nature” of living
matter depends even less on gross chemical composition 2:4 more on rather
subtle differences in the structure of complex protein: ecules. Nuclear
analysis methods are thus even less useful in this case than they are for
detecting the presence of living matter. There is one application in this
connection for which certain radioactive sources might be useful. Suppose
that a certain bio-chemical experiment is devised to detect the presence of
a certain species by measuring the products of the metabolic process (say
COo). Radio isotope (specifically, strong a-particle sources) could be
employed to deliver strong radiation doses to the suspected "living" sample
to see whether the metabolic rate can be changed or even halted. Although
I am not entirely certain of this point, it seems to me that a unique feature
of "living" matter which could be used to establish its presence is that it
can be killed yalabivedy SHAG. Paoddig deéabe, ao sits Wat fav tha cheapest
Dr. Donald Rea -~-2- - July 10, 1964

3) Nature of the Martian Environment. This problem is the only one of the
questions asked by Prof. Lederberg where nuclear methods may have wide ap-
plications. For example, it is possible to obtain a relatively good analysis
of soils using nuclear methods. Both the scattering of fast neutrons (with
observation of prompt gamma rays produced in inelastic collisions) and the
more standard neutron activation methods can be employed. Several flight
packages are now under construction designed for the remote analysis of the
lunar surface. These payloads are intended for use with the "Surveyor"
series space craft. The flight-hardened and environmentally tested instru-
ment packages weigh somewhere between ten and thirty pounds. It is very
probable that, with perhaps minor modifications, these packages could be
used as they are for an analysis of the Martian surface. For example, in+
elastic scattering ‘experiments with fast neutrons could be most useful in
establishing that iron is a prevalent element on the planet's surface. The
most abundant isotope of this element has a particularly large inelastic
scattering cross section and a very conspicuous gamma ray (at 850 keV)

which is easy to observe. I am enclosing some reprints which describe the
possibilities of the method. (In addition, I have asked Dr. James A. Waggoner,
who developed the neutron scattering experiment to provide more detailed
information for you.)

In summary, I would say that neutron analysis methods are not likely to be
useful in actually detecting the presence of life on Mars. However, they
may provide the best means for establishing some pertinent facts about the
nature of the Martian environment.
Very sincerely fk
Hevea Me LOL YL —

Hans Mark

HM:dh