If nuclear fallout takes thousands of years to dissipate, how did the Japanese return to Hiroshima and Nagasaki three months after the nuclear bombs exploded? Doesn’t the area stay radioactive and uninhabitable for thousands of years?
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Atom bombs like the ones dropped on Japan produce two types of radiation: initial and residual. (I’m getting this from Hiroshima and Nagasaki: The Physical, Medical and Social Effects of the Atomic Bombings, an exhaustive Japanese study, published in English in 1981.) Initial radiation is released by the explosion itself. Residual radiation comes later from radionuclides, radioactive isotopes either generated by the explosion or induced in soil, building materials, bodies, etc, by neutron bombardment unleashed by the blast.
The bombs that destroyed Hiroshima and Nagasaki produced their share of residual radiation, but it didn’t stick around long, for two reasons. First, both bombs were detonated more than 500 meters above street level so as to wreak maximum destruction (surrounding buildings would have blocked much of the force of ground-level explosions). That limited surface contamination, since most of the radioactive debris was carried off in the mushroom cloud instead of being embedded in the earth. There was plenty of lethal fallout in the form of “ashes of death” and “black rain,” but it was spread over a fairly wide area.
