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Figure 1.
(A) Histogram of annual yield, in megatons of TNT equivalent, for atmospheric nuclear-bomb tests (UNSCEAR, 2000; USDOE, 2015). Atomic bomb-test yields before the first thermonuclear bomb test in 1952 are too small to plot at the scale shown. Names of some major tests are also shown. Atmospheric testing by the United States (USA) and Union of Soviet Socialist Republics (USSR) ended with the 1963 Partial Test Ban Treaty. Later atmospheric tests were conducted by China and France. (B) Combined 239Pu and 240Pu fallout as calculated from more readily measured 137Cs and 90Sr fallout, with higher (239Pu+240Pu)/137Cs in earlier U.S. (neutron-rich) tests versus later Soviet tests (Koide et al., 1985; UNSCEAR, 2000; Hancock et al., 2014). (C) Graph of 14C as measured in tree rings and in the atmosphere showing the high values measured at sites >45° N and low values measured at sites >10° S before global atmospheric mixing (modified from fig. 4 of Hua et al., 2021).
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