B. L. LARSON AND K. E. EBNER
regard to the implications involved, with the result that the position of milk as an
essential foodstuff, in the opinion of the American public, has been questioned.
The purpose of this review is to evaluate the available data on the accumulation of Sr-90 in milk and other foods and to discuss its significance. This
review will be limited chiefly to the question of long-term radioactive fallout,
since Sr-90 is not an important nuclide in the fallout resulting shortly after a
nuclear explosion.
Background information. It is important for an understanding of the radioactive fallout problem to consider the primary nuclear reactions causing fallout,
and to trace briefly the concern of scientists over the problem as it developed
(191). In its early inception, the major problem was to win the war andlittle
consideration was given to long-range fallout effects on behalf of the general
population. In 1949, Dr. N. M. Smith of Oak Ridge undertook a theoretical
analysis on the long-range aspects of fallout and, as a result, in 1952 Rand
Corporation was given a special contract to make an independent study on the
potential dangers of radioactive fallout. In the summer of 1953, at a conference
called to review the Rand report, it was recommended that a study of mixed
fission products be made, with emphasis being placed on Sr-90. As a result of
this meeting, Project Sunshine was born, with Dr. W. F. Libby as its director.
The immediate aim of this project was to analyze samplesof soil, plants, animals,
dairy products, human bone, and other materials from the United States and
other parts of the world for levels of Sr-90. Originally, Project Sunshine was
coneerned with Sr-90 analyses, but now it is concerned generally with all phases
of the fallout problem.
In late May and early June of 1957, the special Subcommittee on Radiation
of the Joint Committee on Atomic Energy of the Congress of the United States,
held investigations on the nature of radioactive fallout and its effects on man.
Testimony and statements given at these hearings concerned all phases of the
fallout problem and subsequently were published in a comprehensive 2,065-page
report (19). The release of this report made available the first major unclassified
source of information relative to Sr-90 levels in milk, other foods, and forages.
Unfortunately, some of the evidence and conclusions presented were undocumented with data; however, much has appeared in print since that time.
The units used to discuss radioactive phenomena are numerous and are apt
to become co.fusing, since the terminology is not rigorous. The common terms
used, as well as the specifie term used to denote the concentration of Sr-90 in
milk and other materials, are sammarized in the Appendix.
Formation of Strontium-90. The hydrogen bomb uses a small atomic bomb
to trigger the reaction. The atomic bomb is essentially a fission reaction in which
uranium-235 (U-235) is bombarded by neutrons. A simplified scheme of the
reaction may be represented by the following equation, where a neutron (7)
bombards U-235, therebyreleasing fission fragments (f.f.) and 2.5 neutrons, each
containing two million electron volts (19k).
n + U-235 > f.f. + 2.5n (2.0 Mev each)
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