Residual Radioactivity in Neutron-Exposed Objects and Residual Alpha Radioactivity in Black Rain Areas

A Review of Forty-Five Years Study of Hiroshima and Nagasaki Atomic Bomb Survivors I. DOSIMETRY

Abstract

The residual Eu-142 radioactivity due to the atomic bomb explosion in 1945 was first found in 1976 by in-situ high resolution gamma-ray spectrometry at Hiroshima. Since then, various studies on this nuclide have continued not only in Hiroshima but also in Nagasaki and they have contributed to the reevaluation of the neutron dose due to the A-bombing.
By radiochemical separation methods and alpha-ray spectrometry, rather high levels of plutonium were found in the surface soil and in the bottom sediment of water reservoir which were collected at “Black rain area” in Nagasaki.
The U-234/U-238 activity ratios for the uranium leached with 0.1 HNO₃ from the surface of soil samples were found to be relatively higher for the samples which were collected at “Black rain area” in Hiroshima.