Distribution of radionuclides near the Fukushima Dai-ichi Nuclear Power Station

Iijima, Kazuki  ; Sasaki, Takayuki*; Matoba, Daisuke*; Dohi, Terumi   ; Fujiwara, Kenso 

In this study, in order to estimate the on-site distribution, the concentrations of several radionuclides in off-site topsoil were evaluated along six traces of the radioactive plumes, and the characteristic of spatial distribution and depth profile was discussed. The tendency of inventories of Sr-90 and Pu-238 observed in off-site was consistent with that of observed in the previous on-site sampling, indicating that the estimation of on-site distribution of radionuclides based on the off-site was applicable. Concentration of Cs-137 drastically decreased from top of the surface to around 10 cm depth, then gradually decreased, suggesting that Cs-137 was strongly adsorbed at upper part. Surprisingly, the profile of Pu-239+240 was quite different from that of Pu-238, while it was similar to Am-241. It was considered that the behavior of Am-241 was strongly reflected by that of Pu-241, a parent of Am-241, and the deposition event of Pu-239+240 and Pu-241 was different from that of Pu-238.