Plutonium and Cs derived from Nagasaki atomic bomb; The Sedimentation in Nishiyama reservoir for the last 60 years and the distribution in surface soil at present

Kokubu, Yoko   ; Yasuda, Kenichiro   ; Magara, Masaaki  ; Miyamoto, Yutaka   ; Sakurai, Satoshi ; Usuda, Shigekazu; Yamazaki, Hideo*; Yoshikawa, Shusaku*; Nagaoka, Shinji*

In order to determine sedimentation of plutonium and Cs derived from Nagasaki atomic bomb for the last 60 years, we measured Pu/Pu ratio and Pu and Cs concentration in a sediment core collected at Nishiyama reservoir in Nagasaki city. A layer where plutonium and Cs deposited immediately after the detonation was specified in the core. Even at present, the plutonium and Cs from the atomic bomb are continuously being deposited together with those of the atmospheric nuclear tests. We also measured the ratios in soils collected at eastern part of Nagasaki prefecture and Kumamoto prefecture and so on to determine the detailed distributions of the plutonium. The ratios in soils collected in the Shimabara peninsula, Kumamoto city and Aso city were relatively lower than value of global fallout from atmospheric nuclear tests. It indicates that the atomic bomb plutonium was deposited between 2 km and about 100 km east from the hypocenter.