Environmental Radiation Effects Research Group, Research Center for Radiation Protection, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan.
Sci Total Environ. 2010 Nov 1;408(23):5951-7. doi: 10.1016/j.scitotenv.2010.08.054. Epub 2010 Sep 24.
The (239+240)Pu concentrations and (240)Pu/(239)Pu atom ratios were determined by alpha spectrometry and double-focusing SF-ICP-MS for seawater samples obtained in 1984 and 1993 from the Yamato and Tsushima Basins of the Japan Sea in the western North Pacific margin. The total (239+240)Pu inventories in the whole water columns were approximately doubled during the period from 1984 to 1993 in the two basins. The increasing rates were estimated to be 5.1 Bq m(-2)yr(-1) in the Yamato Basin and 4.2 Bq m(-2)yr(-1) in the Tsushima Basin and they corresponded to ~0.02% of the annual (239+240)Pu inflow rate into the Japan Sea through the Tsushima Strait. The mean (240)Pu/(239)Pu atom ratios were ~0.240 and significantly higher than the mean global fallout ratio of 0.18. Furthermore, there were no temporal or spatial variations of (240)Pu/(239)Pu atom ratios during this period in the Japan Sea. The total (239+240)Pu inventories originating from the close-in fallout increased from 17.6 Bq m(-2) to 34.6 Bq m(-2) in the Yamato Basin and from 20.1 Bq m(-2) to 34.6 Bq m(-2) in the Tsushima Basin; however, the relative percentage of ~40% from the close-in fallout was unchanged during this period. A likely mechanism for the increasing Pu inventory would be the continuous inflow of the Tsushima Current from the western North Pacific, and the removal of Pu from surface waters by scavenging onto the settling particles, followed by regeneration of Pu from the settling particles during the downward transport.
本研究采用α谱法和双聚焦 SF-ICP-MS 对 1984 年和 1993 年取自西北太平洋边缘日本海的奄美和对马盆地的海水样品进行了 (239+240)Pu 浓度和 (240)Pu/(239)Pu 原子比测定。在这两个盆地中，1984 年至 1993 年期间，整个水柱中的总 (239+240)Pu 储量增加了约一倍。估计增长率分别为奄美盆地 5.1 Bq m(-2)yr(-1)和对马盆地 4.2 Bq m(-2)yr(-1)，相当于每年 (239+240)Pu 通过对马海峡进入日本海的输入率的0.02%。(240)Pu/(239)Pu 原子比的平均值约为 0.240，明显高于全球沉降的平均值 0.18。此外，在这段时间内，日本海没有 (240)Pu/(239)Pu 原子比的时间或空间变化。来自近距离沉降的总 (239+240)Pu 储量在奄美盆地中从 17.6 Bq m(-2)增加到 34.6 Bq m(-2)，在对马盆地中从 20.1 Bq m(-2)增加到 34.6 Bq m(-2)；然而，在此期间，来自近距离沉降的相对比例保持在40%左右不变。Pu 储量增加的可能机制是日本海西部的对马海流的持续流入，以及 Pu 通过沉降颗粒的吸收入海水中的去除，随后在向下输运过程中，沉降颗粒中再生 Pu。
