Study on discrimination of environmental plutonium

环境中的钚通常由质量数在238至241之间的同位素组成。这些同位素，除了Pu-241 （β -辐射源）外，都是长寿命的α -射线辐射源，具有高放射性毒性。在钚的同位素组成特征中，Pu-240/Pu-239的比值尤其有力地证明了非沉降源Pu的污染。本文主要研究了ICP-MS和TIMS法精确测定Pu-240/Pu-239比值的方法及其应用。对于ICP-MS的测量，考虑了以下因素，得到了满意的结果：1) U内容引入icp应小于十亿分之0.1,2)pu - 240内容必须适应成为超过0.1 ppt, 3)面积(238年阿姆河)必须测量和4)必须注意多元物种Pb和Ar的干扰。另一方面,至于商旅,bacground山峰高质量范围的235年到240年阿姆河被发现在我国航天工具 ... 更错从东京大学,现在减少的背景。因此，需要进一步的研究来精确测量Pu-240/Pu-239的原子比。ICP-MS对前苏联塞米巴拉金斯克核试验场及其周围的土壤样品进行了应用。对300多份土壤样品进行了放射化学分析，并采用常规的α射线光谱仪和ICP-MS进行了测量。结果，虽然总体的铯-137水平与日本的全球沉降物相同或略低，但大多数地点的钚水平比日本的水平高几十到几百倍。Pu-240/Pu-239的比值明显低于普遍接受的全球沉降Pu值0.18。这些地区显然受到了武器级钚的污染。利用乌斯特-卡梅诺戈尔斯克市（试验场以东300公里）样品中的Pu-240/Pu239比值对Pu进行了判别，发现30% -60%的Pu来自SNTS碎片的近距离沉降物Pu。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