Spatial distributions of radionuclides deposited onto ground soil around the Fukushima Dai-ichi Nuclear Power Plant and their temporal change until December 2012

Mikami, Satoshi   ; Maeyama, Takeshi*; Hoshide, Yoshifumi*; Sakamoto, Ryuichi*; Sato, Shoji*; Okuda, Naotoshi*; Demongeot, S.*; Gurriaran, R.*; Uwamino, Yoshitomo*; Kato, Hiroaki*; Fujiwara, Mamoru*; Sato, Tetsuro*; Takemiya, Hiroshi; Saito, Kimiaki  

Comprehensive investigations have been conducted on the land environment affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Distribution maps of Cs-134, Cs-137, and Ag-110m deposition density as of March, September, and December 2012, were constructed according to monitoring results obtained at nearly a thousand locations. Little temporal change of the deposited radionuclides was observed during the nine months from March to December 2012. Weathering effects especially horizontal mobility, during this time were not noticeable. Spatial characteristics in the ratios of Cs-134/Cs-137 and Ag-110m/Cs-137 that deposited on ground were observed by investigations in the Tohoku and Kanto areas. The elaborate deposition maps of Cs-134 and Cs-137 as of September 2012, and those as of December 2012, were constructed using the relationship between the air dose rate and the deposited activity per unit area.