@article{oai:repo.qst.go.jp:00046326,
 author = {Yamada, Masatoshi and Zheng, Jian and 山田 正俊 and 鄭 建},
 issue = {15},
 journal = {Science of The Total Environment},
 month = {Jul},
 note = {The 239+240Pu concentrations and 240Pu/239Pu atom ratios were determined by alpha
spectrometry and double-focusing SF-ICP-MS for seawater samples from two stations,
one at the equator and the other in the equatorial South Pacific Ocean. The 239Pu, 240Pu and 239+240Pu inventories over the depth interval 0-3000 m at the equator station were10.4 +/- 0.5, 8.9 +/- 0.5 and 19.3 +/- 0.9 Bq m-2, respectively. No noticeable difference was observed in 239Pu, 240Pu and 239+240Pu inventories over the depth interval 0-3000 m between the two stations. The total 239+240Pu inventories were significantly higher than that of the expected deposition density of global fallout. The decreasing rates of 239+240Pu over the depth interval 0-1000 m were estimated to be 0.89 +/- 0.07 Bq m-2 yr-1 at the equator station and 0.16 +/- 0.07 Bq m-2 yr-1 at the equatorial South Pacific Ocean station. The obtained 240Pu/239Pu atom ratios in the equatorial Pacific Ocean were higher than the mean global fallout ratio of 0.18. These high atom ratios proved the existence
of close-in tropospheric fallout Pu from the Pacific Proving Grounds (PPG) in the
Marshall Islands. The 239+240Pu inventories originating from the close-in fallout in the full depth of the water column were estimated to be 11.1 Bq m-2 at the equator station and 7.1 Bq m-2 at the equatorial South Pacific Ocean station, and the relative percentages of close-in fallout Pu were 40 % at the former and 34 % at the latter. A significant amount of close-in tropospheric fallout Pu originating from the PPG has been transported to deep layers below the 1000 m depth in the equatorial Pacific Ocean.},
 pages = {20--27},
 title = {239Pu and 240Pu inventories and 240Pu/239Pu atom ratios in the equatorial Pacific Ocean water column},
 volume = {430},
 year = {2012}
}