抄録
There was "black rain" after the Hiroshima atomic bomb (A-bomb) exploded over the Hiroshima city on 6th August 1945. In the Hiroshima black rain area, previous attempts failed to detect fission products such as 137Cs and 90Sr due to global-scale fallout that occurred mainly in 1960s because the global fallout of nuclear test in the atmosphere seemed to contribute larger than the local fallout in 1945. According to unofficial reports, about 51 kg of 235U was loaded in the Hiroshima bomb, of which 912 g was consumed by the 16-kt explosion. Considering that the precise determination of uranium isotopic composition will give some information about radioactive equilibrium, enrichment of 235U or presence of 236U, thermal ionization mass spectrometry (TIMS) and accelerator mass spectrometry (AMS) have been employed to detect uranium isotopes from the Hiroshima A-bomb in soil samples previously collected in 1976 from the black rain area around the Hiroshima city. The results of uranium isotope measurements as well as inter comparison between TIMS and AMS will be presented. The 236U measurement can provide valuable information about the local fallout contamination by the Hiroshima A-bomb.
