量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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The marine environment is complex, and it is desirable to have measurements for seawater samples collected at the early stage after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident to determine the impact of Fukushima-derived radionuclides on this environment. Here Pu isotopes in seawater collected 33-163 km from the FDNPP site at the very early stage after the accident were determined (May 2011, within two months after the accident). The distribution and temporal variation of 239Pu and 240Pu were studied. The results indicated that both 239+240Pu activity concentrations (from 0.81±0.16 to 11.18±1.28 mBq/m3) and 240Pu/239Pu atom ratios (from 0.216±0.032 to 0.308±0.036) in these seawater samples were within the corresponding background ranges before the accident, and this suggested that Fukushima-derived Pu isotopes, if any, were in too limited amount to be distinguished from the background level in the seawater. The analysis of Pu isotopic composition indicated that the major sources of Pu in the seawater after the accident were still global fallout and the Pacific Proving Ground close-in fallout. The contribution analysis showed that the contributions of the Pacific Proving Ground close-in fallout in the water column of the study area ranged from 26% to 77% with the average being 48%.
Pu isotopes in the seawater off Fukushima Daiichi Nuclear Power Plant site within two months after the severe nuclear accident
