PLUTONIUM RELEASED BY THE NAGASAKI A-BOMB - MOBILITY IN THE ENVIRONMENT
PLUTONIUM RELEASED BY THE NAGASAKI A-BOMB - MOBILITY IN THE ENVIRONMENT
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DOI：
10.1016/0969-8043(95)00161-6
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发表时间：
1995-11-01
影响因子：
1.6
通讯作者：
KUDO, A
中科院分区：
文献类型：
--
作者：
MAHARA, Y;KUDO, A
第一次和第二次人造钚-239 + 240的环境释放来自1945年在阿拉马戈多和长崎的核爆炸。长崎的释放比阿拉马戈多更为严重，因为它发生在人口密度高的地区。未裂变的Pu-239 + 240和各种裂变产物（例如Sr-90和Cs-137）在潮湿和温和的条件下与各种环境材料（土壤，沉积物和植物）相互作用超过45年。为了评估Pu-239 + 240的环境迁移性，在西山（震源以东3公里）调查了这次释放的放射性核素的分布，核爆炸后30分钟，含有未裂变钚和裂变产物的黑色大雨落下。在450 cm深的非饱和土柱中测定了Sr-90、Cs-137和Pu-239 + 240的垂直分布。大多数放射性核素存在于距地面30 cm的土柱中（95%的Sr-90、99%的Cs-137和97%的Pu-239 + 240）。然而，Sr-90和Pu-239 + 240在地下水中检测到，以及低于200厘米的深度。在距地表40 cm以下和地下水中未发现Cs-137。这些观测结果表明，大约3%的Pu-239 + 240在土壤中的迁移速度比其余的Pu-239 + 240快。从西山水库采集的沉积物岩心中发现了Cs-137和Pu-239 + 240的尖峰，表明1945年长崎当地沉降物的重沉积。另一方面，由于Sr-90在淡水沉积物中是移动的，因此在沉积物芯中没有1945 Sr-90峰。Pu-239 + 240峰在1945年前的沉积物岩心中意外发现。虽然Sr-90在这些剖面中被发现，但没有发现Cs-137。与沉积物柱芯中的分布相反，Cs-137在树木年轮中通过扩散从树皮向树的中心扩散，而没有沉降记录。大部分Pu-239 + 240分布在树木年轮中，其沉积记录与沉积物芯中的记录相似。此外，在1945年以前的树木年轮中意外地发现了非常少量的Pu-239 + 240（约1%）。对这些意外发现的唯一合理解释是环境中存在移动的Pu-239 + 240。
The first and second environmental releases of man-made Pu-239 + 240 came from nuclear explosions at Alamagordo and Nagasaki in 1945. The release at Nagasaki was more serious than at Alamagordo, because it happened in an area with a high population density. Unfissioned Pu-239 + 240 and various fission products (e.g. Sr-90 and Cs-137) have been interacting here with various environmental materials (soils, sediments, and plants) under wet and temperate conditions for more than 45 years. To assess the environmental mobility of Pu-239 + 240, the distributions of radionuclides from this release were investigated at Nishiyama (3 km east of the hypocenter) where heavy black rain containing unfissioned plutonium and fission products fell 30 minutes after the nuclear explosion. The vertical distributions of Sr-90, Cs-137 and Pu-239 + 240 were determined in unsaturated soil cores up to 450 cm deep. Most radionuclides were found in the soil column 30 cm from the ground surface (95% of Sr-90, 99% of Cs-137 and 97% of Pu-239 + 240). However, Sr-90 and Pu-239 + 240 were detected in the groundwater as well below a depth of 200 cm. No Cs-137 was found below 40 cm from the ground surface or in groundwater. These observations reveal that about 3% of the total Pu-239 + 240 has been migrating in the soil at a faster rate than the remaining Pu-239 + 240. Sharp peak of Cs-137 and Pu-239 + 240, indicating heavy deposition from the Nagasaki local fallout of 1945, were found in sediment cores collected from the Nishiyama reservoir. On the other hand, since Sr-90 is mobile in fresh water sediments, there was no 1945 Sr-90 peak in the sediment cores. Pu-239 + 240 peaks were unexpectedly discovered in pre-1945 sediment core sections. Although Sr-90 was found in these sections, no Cs-137 was found. By contrast to the distribution in sediment cores, Cs-137 in tree rings had spread by diffusion from the bark to the center of the tree without holding a fallout deposition record. Most of the Pu-239 + 240 was distributed in the tree rings following a similar deposition record to that found in sediment cores. Furthermore, a very small amount of Pu-239 + 240 (about 1%) was found unexpectedly in pre-1945 tree rings. The only reasonable explanation for these unexpected discoveries is the existence of mobile Pu-239 + 240 in the environment.