学術雑誌論文 Vertical distributions of Pu and radiocesium isotopes in sediments from Lake Inba after the Fukushima Daiichi Nuclear Power Plant accident: source identification and accumulation

Cao, Liguo  ,  Ishii, Nobuyoshi  ,  Zheng, Jian  ,  Kagami, Maiko  ,  Pan, Shaoming  ,  Tagami, Keiko  ,  Uchida, Shigeo

78pp.287 - 294 , 2017-01 , Elsevier
内容記述
Amounts of radiocesium were released into the environment due to the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, which resulted from the massive Tohoku earthquake on 11 March 2011. Lake Inba in Chiba Prefecture locates about 200 km away from the FDNPP site and the lake was contaminated by radioactivity from the accident. In the present study, the vertical distributions and accumulations of radiocesium and Pu isotopes were investigated in sediment cores collected during 2011-2015. The results showed that the observed 134Cs/137Cs activity ratios in the core samples were approximately 1, suggesting that sediment samples were contaminated by the FDNPP-released radiocesium. The calculated higher radiocesium inventories of the collected sediment cores indicated that most of these radiocesium was subsequently accumulated in the lake, suggested that radiocesium input was greater than the output. The 239+240Pu activities in the sediments were all within background level before the accident. The atom ratios of 240Pu/239Pu ranged from 0.175 to 0.210, suggesting that Pu originated from global stratospheric fallout rather than the FDNPP accident from the FDNPP accident; meanwhile, the observed global fallout 240Pu/239Pu atom ratio in Inba lake sediments also indicated that close-in Pu from the Pacific Proving Grounds source were not delivered to the regions above 36 ºN via early tropospheric fallout.

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