铀颗粒物中~(235)U/~(238)U的LA-MC-ICP-MS分析技术研究

为满足核保障和核取证中含铀颗粒物分析的需求,建立了激光剥蚀-多接收电感耦合等离子体质谱(LA-MC-ICP-MS)测定铀颗粒物中~(235)U/~(238)U值的方法,并研究了铀颗粒物样品的装载、质量分馏的影响因素和校正方法,以及粒径10μm以下铀颗粒物的定位和分析等关键技术问题。建立了基于GBW04234的外标标准化法、基于膜去溶和LA-MC-ICP-MS联用的标准样品交叉法(SSB法)两种质量分馏校正技术,该方法对CRM124-1中~(235)U/~(238)U测量结果的相对扩展不确定度小于0.14%(k=2),测量结果与参考值在不确定度范围内一致。用显微操纵技术将颗粒物转移至覆盖定位铜网的导电胶表面,解决了微米级铀颗粒物的装载和定位问题,通过优化参数,实现了粒径5μm铀颗粒物中~(235) U/~(238)U比值的准确测量,测量结果的相对扩展不确定度小于0.64%(k=2)。

Determination of 235U/238U Ratio in Uranium Particles by Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry

Analysis of uranium particles is extremely important for nuclear safeguards and nuclear forensics. This work described the technical advancements for the direct analysis of ²³⁵U/²³⁸U ratios in uranium particles by laser ablation multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS), including loading and localization of uranium particles, evaluation and correction of mass fractionation, analysis of particles smaller than 10 μm. Micrometer-sized uranium particles could be efficiently transferred to a tape covered with copper net by using micromanipulation method. Two methods, including the external standardization method based on GBW04234 and standard sample bracketing (SSB) method based on the combination LA-MC-ICP-MS with DSN (Desolution Nebulizer), were established to correct the mass fractionation. The analytical results show that the relative expanded uncertainty of²³⁵U/²³⁸U isotope ratio in CRM124-1 samples is less than 0.14% (k=2), and the results agree with certificated value within uncertainty range. The LA-MC-ICP-MS technique developed offers an accurate and precise possibility for the²³⁵U/²³⁸U ratio determination of uranium particles with size down to 5 μm. The relative expanded uncertainty of 0.64% (k=2) is achievable.