Radioactive fallout Cs-137 and U-235 isotopes in the black rain by the Hiroshima atomic bomb

Abstract

Early radiation surveys and sample measurements just after the bombing that the radioactive fallout from the Hiroshima atomic bomb has revealed that high radioactive contamination at the Koi-Takasu area located about 3 km west of the hypocenter. However, global fallout due to the nuclear test contaminated radioactivity originated to the atomic bomb. We have analyzed some small pieces obtained from plastered walls which has Black Rain streaks on it.The house located 3.7 km west to the hypocenter and the tainted part of the wall was cut and donated to Hiroshima Peace Museum in May, 2000.We applied gamma-ray spectrometry by a low-background Ge detector to detect Cs-137 and U-235 abundance by ICP-MS.It has shown that U-235/U-238 ratio in the black part of the wall was higher than natural ratio. The atom ratio Cs-137/U-235 was compared to the fission yield ratio. Some discussion of fractionation will be given.