has been derived from the period of intensive nuclear testing in the
atmosphere during the 1950's and early 1960's. It is estimated that more
than 500 megatons of nuclear yield were detonated in the atmosphere between
1945 and 1971, about half of this yield being produced by a fission
reaction. The peak occurred in 1961-62, when a total of 340 megatons were
detonated in the atmosphere by the United States and Soviet Union. The
limited nuclear test ban treaty of 1963 ended atmospheric testing for the
United States, Britain, and the Soviet Union, but two major
non-signatories, France and China, continued nuclear testing at the rate of
about 5 megatons annually. (France now conducts its nuclear tests
underground.)

A U.N. scientific committee has estimated that the cumulative per capita
dose to the world's population up to the year 2000 as a result of
atmospheric testing through 1970 (cutoff date of the study) will be the
equivalent of 2 years' exposure to natural background radiation on the
earth's surface. For the bulk of the world's population, internal and
external radiation doses of natural origin amount to less than one-tenth
rad annually. Thus nuclear testing to date does not appear to pose a
severe radiation threat in global terms. But a nuclear war releasing 10 or
100 times the total yield of all previous weapons tests could pose a far
greater worldwide threat.

The biological effects of all forms of ionizing radiation have been
calculated within broad ranges by the National Academy of Sciences. Based
on these calculations, fallout from the 500-plus megatons of nuclear
testing through 1970 will produce between 2 and 25 cases of genetic disease
per million live births in the next generation. This means that between 3
and 50 persons per billion births in the post-testing generation will have
genetic damage for each megaton of nuclear yield exploded. With similar