Geochemical Journal, Vol. 46 (No. 4), pp. 341-353, 2012
M. Yamamoto,1 T. Takada,1 S. Nagao,1 T. Koike,2 K. Shimada,3 M. Hoshi,4 K. Zhumadilov,4 T. Shima,5 M. Fukuoka,5 T. Imanaka,6 S. Endo,7 A. Sakaguchi8 and S. Kimura9
1Low Level Radioactivity Laboratory, Kanazawa Univ., Ishikawa 923-1224, Japan
2Graduate School of Science, Tohoku Univ., Sendai, Miyagi 980-8578, Japan
3Cyclotron Radioisotope Center, Tohoku Univ., Sendai, Miyagi 980-8578, Japan
4Research Institute for Radiation Biology and Medicine, Hiroshima Univ., Hiroshima 734-8553, Japan
5Research Center of Nuclear Physics, Osaka Univ., Ibaraki, Osaka 567-0047, Japan
6Research Reactor Institute, Kyoto Univ., Kumatori-cho, Osaka 590-0494, Japan
7Graduate School of Engineering, Hiroshima Univ., Higashi-Hiroshima 739-8527, Japan
8Graduate School of Science, Hiroshima Univ., Higashi-Hiroshima 739-8527, Japan
9School of Medicine, Dokkyo Medical Univ., Tochigi 321-0293, Japan
(Received February 3, 2012; Accepted June 21, 2012)
A field survey was carried out soon after the Fukushima Dai-ichi Nuclear Power Plant accident. Gamma-ray emitting radionuclides and plutonium isotopes in a series of soil samples collected from the heavily contaminated areas outside the 20-km exclusion zone, as well as from Okuma Town adjacent to the plant, were measured.
Volatile radionuclides such as 131I, 134Cs, and 137Cs contributed largely to the released radioactivity. Higher depositions of these nuclides were observed in areas to the northwesternincluding Okuma Town and Iitate Village, which is at a distance of 25-45 km from the plant. The results obtained were consistent with the levels and distributions estimated later by the Japan-USA joint-survey (Asahi Shimbun Company, 2011). Trace amounts of plutonium isotopes originating from the accident were detected mainly in soil samples from Iitate Village and in limited soil samples from Okuma Town. The detected levels of 239,240Pu contamination due to the accident were considered to be less than a millionth those of the 137Cs contamination.
Key words: Fukushima Dai-ichi Nuclear Power Plant accident, early field survey, soil contamination, gamma-emitting radionuclides, plutonium