激光烧蚀-多接收电感耦合等离子体质谱法测定铀颗粒物中铅杂质的同位素比值

Isotopic Abundance Analysis of Lead in Uranium Particles by Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry

为有效获取铀颗粒物中具有取证价值的铅杂质同位素信息,建立了激光烧蚀-多接收电感耦合等离子体质谱(LA-MC-ICP-MS)测定铀颗粒物中铅杂质同位素比值的方法。探究了诸多同位素分馏效应校正方法下铅本底对同位素测量的影响,选用的LA-MC-ICP-MS系统的本底对比值测量结果的影响小于0.001(^(208)Pb的信号强度大于2.2×10~3cps),确定采用NIST SRM612为外标校正质量分馏,固定激光束斑直径30μm、脉冲重复率20 Hz、调节能量密度使LA-MC-ICP-MS分析NIST SRM612和铀颗粒物样品所得208Pb分别小于1.5×10~5cps和3×10~4cps,标准物质CRM124-4样品中^(206)Pb/^(208)Pb、^(206)Pb/^(207)Pb和^(207)Pb/^(208)Pb比值测量结果的相对实验标准不确定度小于0.48%、0.68%和0.40%。实际样品分析结果表明,本方法可有效区分铀颗粒物中的铅同位素比值差异,有助于鉴别其来源。

The isotopic abundance of lead as a signature or fingerprint in uranium has played an important role in nuclear forensics analysis. In this work, a novel analytical approach is presented to determine the isotopic abundance of lead in uranium particles by laser ablation multiple collector inductively coupled plasma mass spectrometry （LA-MC-ICP-MS）. External standardization method is involved in correcting the mass fractionation in the process of analysis. The approach has been successfully validated by the measurement of CRM124-4 standard reference material. Spot size and ablation rate are set at 30 μm and 20 Hz, respectively. Laser energy density is under control to ensure that the 208^Pb for NIST SRM612 and uranium particles are less than 1.5×10^5 cps and 3 ×10^4 cps, respectively. The results show that the relative uncertainty of 206^pb/208^Pb, 206^pb/207^pb and 207^pb/208^pb ratios in CRM124-4 are less than 0.48% , 0.68% and 0.40% , respectively. Two kinds of uranium particles originated from different places have been analyzed by the proposed approach. The results demonstrate that the distinct lead isotope signatures can offer a number of evidence to determine whether the uranium particles have come directly from a mining operation or an ore-body, or whether it is anthropogenic.