A euphemstically named unit of body burden of strontium-90, = 1 nanocurie of strontium-90 per kilogram of calcium.
Libby reported a recent estimate that the maximum permissable concentration of strontium-90 in the human body was about one microcurie per 1000 grams of calcium.⁵ To help calculate total body burden, scientists had devised a convenient measure called a Sunshine unit, which was 0.001 of the permissible adult body burden. Thus, ten Sunshine units were comparable to natural background radiation. One thousand Sunshine units were not expected to produce any visible skeletal damage, but ten thousand units might be hazardous. Children under seven years of age were most susceptible to strontium-90, but absorption by adults over 40 was negligible. Measurements made in Houston, Texas, on bones of deceased children indicated an average strontium-90 content of 0.4 to 0.6 Sunshine units.⁶
5. Willard F. Libby, “The Radioactive Fallout and Radioactive Strontium,” paper presented at Northwestern University, Evanston, IL, Jan. 19, 1956, AEC.
6. GAC 48, Jan. 12-13, 1967,AEC. [GAC is the General Advisory Committee to the AEC]
Richard G. Hewlett and Jack M. Holt.
Atoms for Peace and War, 1953-1961: Eisenhower and the Atomic Energy Commission.
Berkeley : University of California Press, 1989.
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