Study on discrimination of environmental plutonium

环境中的钚通常由质量数从238到241的同位素组成。这些同位素，除了Pu-241（β-发射体），都是具有高放射性毒性的长寿命α射线发射体。在钚的同位素组成特征中，Pu-240/Pu-239的比率特别有力地证明了非沉降物来源的钚造成的污染。本文着重研究了用ICP-MS和TIMS精确测定Pu-240/Pu-239比值的方法及其应用。1）引入ICP-MS的U含量应小于0.1 ppb，2）Pu-240含量必须调整为大于0.1 ppt，3）必须测量质量面积（238 amu）和4）必须注意多原子物种与Pb和Ar的干扰。另一方面，对于TIMS，在235至240 amu的质量范围内的高背景峰在仪器转移中被检测到， ...更多信息 从东京大学毕业，现在进行背景还原。因此，需要进一步研究精确测量Pu-240/Pu-239原子比。对300多个土壤样品进行了放射化学分析，并通过普通的α射线光谱仪和ICP-MS进行了测量。结果表明，虽然总体Cs-137水平与日本全球沉降物相同或略低，但大多数地点的钚水平比日本高出数十至数百倍。Pu-240/Pu-239的比率大大低于全球沉降物Pu的普遍接受值0.18。这些区域显然受到武器级钚的污染。从乌斯季-卡缅诺戈尔斯克市（试验场以东300公里）的样品中，用Pu-240/Pu-239的比值对Pu进行了鉴别。发现总Pu中有30-60%的部分是由SNTS碎片的近距离落尘Pu造成的。少

Plutonium in the environment is generally composed of isotopes of mass numbers ranging from 238 to 241. These isotopes, except Pu-241 (beta-emitter), are all long-lived alpha-ray emitters with high radiotoxicites. Of the characteristics for isotopic composition of Pu, the ratio of Pu-240/Pu-239 particularly gives strong evidence of the contamination due to Pu of non-fallout origin. This work was focused on the studies for developing the precise measurement of Pu-240/Pu-239 ratio by ICP-MS and TIMS and their application.As for ICP-MS measurmenet, satisfactory results were obtaind wit the following consideration : 1) U contents introduced into the ICP-MS should be less than 0.1 ppb, 2) Pu-240 content must be adjust to become more than 0.1 ppt, 3) mass area (238 amu) must be measured and 4) care must be taken for interference of polyatomic species with Pb and Ar. On the other hand, as for TIMS, high bacground peaks in the mass range of 235 to 240 amu were detected in the instrument transf … More erred from Tokyo Univ., and now reducing of background is conducted. Therefore, further studies are needed for precise measurement of the Pu-240/Pu-239 atomic ratio.Application of ICP-MS was done for soil samples in and around the former Soviet Union's Semipalatinsk nuclear test site. More than 300 soil samples were subjected to radiochemical analysis, and measured by usual alpha-ray spectrometer and ICP-MS.As a results, while the overall Cs-137 levels were as same as or slightly lower than Japanese global fallout, Pu levels in most of sites were several ten to several hundred times higher than the Japanese level. The ratios of Pu-240/Pu-239 were significantly lower than the value of 0.18 commonly accepted for global fallout Pu. These areas are clearly contaminated with weapon-grade Pu. Discrmination of Pu was performed using the Pu-240/Pu239 ratio in the samples from Ust'-kamenogorsk City (300 km east of test site) It was found thata fraction of 30-60% of total Pu were due to the close-in fallout Pu from the SNTS debris. Less