a
Mamorendum For Dr. Lithy, Comiissionsr, United Stetes Atomic Energy
Comzission,
Operations
Subj: (U) Measurement of Local Fall-Out in Atomic Energy
this tire. I want to stress thet the best wey and perhaps the only
way of measuring the many unknowns of fell-out would be to detonate
a 100 KT clean device in our country, within our own test site, on
dry land so that we can study all aspects of the fall-out in great
detail. Since at the present time we cannot detonate anything above
1 KT of fission yield on the surface in the Nevada Test Site, we are
forced to study fall-out in the Tacifie Proving Ground. fd]
3.
Measurement of Local Fall-out in the Pecific Proving
Ground
a. Since the PPG is mostly water, we have a great deal of
difficulty in measuring the fall-out which gets deposited on the water
ané which then sinks with different rates of Sall, which dissolves
with different rates o° solubility, eni wiich comes under the influence
of the ocean currents which can be measured with differant degrees of
accuracy. We must also ameider the mixing of the ocean water by the
surface waves (as indicated by you) an3 what may be even more dis-
couraging, we must also consider zones of divergence and convergence in
the ocean similer to such an effect in the atmosphere where water may
rise or fall in a large seale circulation in the vertical direction, I
am amazed and pleased with the measurements of Scripps. Apperertly, they
have develcped a method which can determine the order of magnitude of the
totel percentege of fall-out by oceanogravhic sampling methods.
However,
I question whether this system could ever be improved to a point where it
measures with sufficient degree of accuracy, the extent of the local
fall-out so that we can be advised of what i= lef for intermediate and
long range world-wide fall-out. A study of all past test operations in
the PFG has borne out the fact thet it is next to impossible to determine
with any degres of accuracy the total percentage of gross fall-out. The
Sr?° faliout is subject to even greater errors of measurement at the PPG.
b. The accident of CASTLE PRAVO is an exception to this rule.
Here the Japanese in a 99 ton fishing vessel were able to scoop up end
put into cellophane bags handSulls of the fall-out material 75 to &5
miles downwind of ground zero. In this same CASTLE accident some of the
islands to the east of the Bikini ceme under excessive fall-out which may
be surveyed even today for possible fission products or Sr 0 content and
for other measurements well known to you, Put this was an accident.
Accidental though it may have been, it represented very good sampling for
the few scmpling st-tions such as the “ishing vessel and the few islands
involved, I am afraid, Dr. Libby, that this problem of measuring total
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