原爆投下1分後――消された残留放射線の影響――

抄録

After the detonation of the atomic bomb in Hiroshima and Nagasaki, many people were exposed to the blast, heat and initial radiation. In addition to these people, many more people were exposed to the residual radiation which came from black rain, water and food, radioactive dust and so on. In 1947, the Atomic Bomb Casualty Commission was established by the Presidential Order of Harry Truman for research on people exposed to the Atomic Bomb. This article focuses on how the U. S. Government handled the facts about residual radiation and how ABCC scientists discussed it in the 1940s and 50s.

On September 5, 1945, Wilfred Burchett, a correspondent for the Daily Express, based on data gathered in Hiroshima reported as follows: “People are still dying, mysteriously and horribly―people who were uninjured in the cataclysm―from an unknown something which I can only describe as the atomic plague.” Concerned about this report, Brigadier General F. Thomas Farrell, chief of the War Department’s atomic bomb mission (Manhattan Project), issued a statement denying that the damage was from radiation. He said, “the atomic bombs dropped on Hiroshima and Nagasaki were detonated at such a high altitude that no radiation remained, and that even if some people died later, it was because of injuries sustained at the time of the explosion.” According to The New York Times on September 13, 1945, he said, “The weapon’s chief effect was blast" and that "his group of scientists" found no evidence of continuing radioactivity in the blasted area on Sep. 9 when they began their investigation.

After this statement, the Manhattan Engineer district continued an investigation of residual radiation in Hiroshima and Nagasaki. Mentioning the data which were collected in late September and early October 1945, they concluded, “No harmful amount of persistent radioactivity was present after the explosion.”

However, in 1950, scientists of ABCC noticed the effects of residual radiation and started the “Residual Radiation Survey” by collecting information on the people who had radiation signs and symptoms after entering the city after the bombing. However, according to Lowell Woodbury, physician in the statistic department of the ABCC, “Due to pressure of other work and a shortage of investigators, this project was not actually initiated.”

Woodbury pointed out the possibility that “The black rain left a deposit sufficiently radioactive to cause radiation signs and symptoms in extremely sensitive individuals, and that deposit was largely washed away in the September rains and typhoon,” and the necessity of more detailed investigations. But this investigation was not conducted. On the other hand, the conclusion of the Manhattan District Report, “No harmful effect of residual radiation in Hiroshima and Nagasaki,” even though it was conducted after the typhoon and rains, is still the standard which is applied today.

The US government has continuously denied the influence of residual radiation in Hiroshima and Nagasaki. However this official view was not based on detailed scientific research.