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 of ²³⁵U/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 the ²³⁵U/²³⁸U ratio determination of uranium particles with size down to 5 μm. The relative expanded uncertainty of 0.64% (k=2) is achievable.