Date

Jun 20, 1946

Description

This highly technical report on residual radioactivity by the Naval Medical Research Institute at Bethesda complemented the work of the Naval Medical Mission on the same topic. It found that the “deposition of fission products” (not yet called fallout) from the atomic bombings produced residual radiation in areas around Hiroshima and Nagasaki. The other source of residual radioactivity was “the production of radioactive isotopes in the ground materials by the extremely intense neutron and gamma ray production incident to the explosion.”

Two areas of Hiroshima and Nagasaki received close scrutiny. One was the village of Takasu, downwind from Hiroshima. There, the “residual activity in the Hiroshima area as a whole was far below physiologically significant intensity.” In the Nishiyama area of Nagasaki, however, the report found that “the maximal tolerance dose of radiation was exceeded for a sufficient length of time … to produce significant physiological effects but that it fell below the maximal tolerance dose fairly quickly.” Further research by Japanese experts with Kyushu Imperial University found “significant, although slight physiological effects” that were “capable of producing a measurable physiological change.”

Source

RG 77, Reports Pertaining to the Effects of the Atomic Bomb 1945-1946, box 90

Document published in following posting(s):

80th Anniversary of the Atomic Bombings: Revisiting the Record

Sep 25, 2025