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東部太平洋における$$^{241}$$Amの分布と沈降挙動

Distribution and settling behavior of americium-241 in the tropical East Pacific

木下 哲一*; 永岡 美佳  

Kinoshita, Norikazu*; Nagaoka, Mika

大気圏内核実験により放出された$$^{241}$$Puの壊変生成物である$$^{241}$$Amの熱帯東太平洋における水平及び垂直移動を解明するために、分布を調査した。2003年に採取した海水試料の$$^{241}$$Am濃度を測定し、既に得られている$$^{239+240}$$Pu結果と比較した。その鉛直分布は$$^{239+240}$$Puと同様であったが、一部地点では、極大濃度が$$^{239+240}$$Puよりも100mから200m深いところで観測された。また、$$^{241}$$Amの鉛直分布について、$$^{241}$$Puからの壊変、懸濁粒子への吸着、沈降挙動をボックスモデルを用いて濃度極大深度が説明できた。

The distribution of the anthropogenic radionuclide americium-241 ($$^{241}$$Am), a decay product of $$^{241}$$Pu discharged from atmospheric tests of nuclear weapons, was investigated to resolve its horizontal and vertical migration in the Tropical East Pacific. We analyzed $$^{241}$$Am concentrations in seawater samples collected in 2003. On comparing the $$^{241}$$Am concentrations with the previously determined concentrations of $$^{239+240}$$Pu in the same samples, the vertical profiles of $$^{241}$$Am were found to be similar to those of $$^{239+240}$$Pu. At some stations, the maximum concentration of $$^{241}$$Am occurred 100-200 m deeper than that of $$^{239+240}$$Pu. In addition, the $$^{241}$$Am vertical profile was explained by using a box model that considers the decay of $$^{241}$$Pu and adsorption and scavenging by suspended particles and the residence time of $$^{241}$$Am in the Pacific was also estimated by using the model.

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