Development of dose evaluation method for confirmation of completion of decommissioning, 2; Identification of radiocesium origin using Cs/Cs isotope ratio

Shimada, Asako ; Tsukahara, Takehiko*; Nomura, Masao*; Kim, M. S.*; Shimada, Taro ; Takeda, Seiji ; Yamaguchi, Tetsuji 

Radiocesium from the Fukushima Daiichi Nuclear Power Station (1F) accident can be treated as background radioactivity at completion of decommissioning, so determining the origin of radiocesium is essential. Therefore, we studied identification of radiocesium origin using Cs/Cs isotope ratio. The ratio originated from 1F was 0.36280.0005. When the ratio originated from decommissioning facility was 0.050.2 larger than that originated from 1F, it is challenging to decrease the stand deviation less than 0.01 for 1 Bq/g of Cs because precision was decreased as decreasing the Cs concentration. If the ratio is able to be determined within the standard deviation of 0.0005 for 0.5 Bq/g of soil sample, the identification would be available.