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DOE ARC ailv
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Part Vil
Biology and Medicine
Radioactive Fallout Studies (Project SUNSHINE) gigaqeuaaumemmall
Information continues to be accumulated on the worldwide fallout of radioactive strontium,
its accumulation in the soil, its incorporation into the food chain, and its deposition into the
human body, principally in the skeleton. Representatives of the United States, United Kingdom,
and Canada, meeting informally on October 18 and 19, found themselves in substantial agreement on methods of measurement and, in those cases where observations are comparable, on
results obtained.
As the broader outlines of the fallout problem become better defined, an increasing proportion of the total research effort is required for reducing the degree of uncertainty which
still remains in present knowledge of the distribution of fallout and the physical and chemical
behavior of strontium. Some of the uncertainties arise from physical and geographical factors
such as the vastness of the earth, the relative inaccessibility of both the stratosphere and many
geographical areas, and difficulties of estimating fallout into the ocean. Some depend upon the
technical difficulties in obtaining and measuring samples. Other uncertainties are the result of
lack of information on many details of nature upon which the questions involved in SUNSHINE
serve to focus attention, perhaps for the first time.
Estimates of the results of detonations of nuclear weapons to date, in terms-of both the
present and future distribution of strontium 90 in nature and in man, must be considered as
tentative and to require additional measurements. In the opinion of Commissioner Libby and the
staff, estimates made by persons actively engaged in the SUNSHINE program are believed to be
generally somewhat conservative or “on the safe side.”
In a recent address before the American Association for the Advancementof Science,
Washington, D. C., October 12, Commissioner Willard F. Libby has estimated that “a total of
about 22 millicuries per square mile of strontium 90 is to be found in the soils of the midwestern United States,” and that the concentration is about three quarters of this value in
similar latitudes in the rest of the world. “The stratospheric deposition would be expected to
continue at the expected rate which at the present is about {.2 millicuries per year, so that
some 15 years from now ...a maximum additional total stratospheric fallout of about 6 millicuries per square mile will have occurred. In the meantime, the present 22 millicuries per
square mile would have been reduced to 15 by radioactive decay, just about compensating for
the stratospheric deposition.” From available data relating human uptake to content of the soil,
he estimates that “at the moment we would expect that the body burden for children born now in
America eventually would amount to between 0.004 MPC units [4 micromicrocuries per gram]
. ..and possibly a figure two or three times higher.”
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