ICP-MS analysis of environmental plutonium

摘要

ICP-MS was applied to determine the concentration of ~(239)Pu and ~(240)Pu and their isotope ratio in environmental samples. Two types of chromatographic resins, Dowex 1X8 and TEVA, were examined for their applicability to the separation of Pu from the matrix elements. Sufficient decontamination factors (10~4-10~5) for many matrix elements including U, which interferes with the detection of mass 239, were obtained with both resins. The detection limit of Pu by quadrupole-type ICP-MS was about 0.02 pg ml_(-1) in the sample solution. High resolution-type ICP-MS was also tested for its sensitivity and the detection limit was found to be about one order of magnitude better than this value. Analytical results of ~(239+240)Pu in standard reference materials (IAEA-134, -135, -367, -368 and -SOIL-6) indicated that the accuracy of the method was satisfactory. Data on the ~(240)Pu/~(239)Pu atom ratios in these reference materials, which are scarce in the literature, were also obtained. Compared with alpha-spectrometry, the ICP-MS method has significant advantages in terms of prompt measurement time, simple analytical procedures and capability of determining the ~(240)Pu/~(239)Pu ratio. The ~(240)Pu/~(239)Pu atom ratios observed in seven soil samples collected from different places in Japan ranged from 0.168 to 0.181, which are comparable to the global fallout ratio. Analytical results for samples originating from different places worldwide (including contaminated areas) showed a wide range of the ~(240)Pu/~(239)Pu atom ratio (0.04-0.4) according to the source of the Pu. Determination of the ~(240)Pu/~(239)Pu ratio is useful to identify the origin of the contamination.