UNCLASSIFIED Part VII . 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 factor such as the vastness of the earth, the relative inaccessibility of both the stratosphere and geographical areas, and difficulties of estimating fallout into the ocean. Some depend upon th technical difficulties in obtaining and measuring samples. Other uncertainties are the result Bf 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 weaponsto 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 ffhe dat Larienee ah chtech teahtiansbaa er lite staff, estimates made by persons actively engaged in the SUNSHINE program are believed to generally somewhat conservative or “on the safe side.” - In a recent address before the American Association forthe Advancementof Science, Washington, D. C., October 12, Commissioner Willard F. Libby has estimated that “a total about 22 millicuries per square mile of strontium 90 is to be found in the soils of the mid- aie RN pte ge western 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 continue at the expected rate which at the present is about 1.2 millicuries per year, so that some 15 years from now . . . a maximum additional total stratospheric fallout of about 6 mili curies per square mile will have occurred. In fhe meantime, the present 22 millicuries per square mile would have been reduced to 15 by radioactive decay, just about:compensating f the stratospheric deposition.” From available data relating human uptake tocontent of the he estimates that “at the moment we would expéct that the body burden for’ children born no America eventually would amount to between 0.004 MPC units [4 micromicrocuries per gra . and possibly a figure two or three times higher.” UNCLASSIFIED. Be — As thebroader outlines of the fallout problem become better defined, an increasing pro- portion of the total research effort is required for reducing the degree of uncertainty. which rs _ 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 intothe human body, principallyin the skeleton. Representatives of the United States, United Kingdom and Canada, meeting informally on October 18 and 19, found themselves in substantial agreement on methodsof measurement and, in those cases where observations are comparable, on results obtained. OeET A Se TRTET welle FE EPwae fa. TenOTP Tie?MEee Radioactive Fallout Studies(Project SUNSHINE) (UNCLASSIFIED) - wae Biology and Medicine