The use of solution nebulization ICP-MS combined with particle screening and micro-sampling for analysis of individual uranium-bearing particles

Abstract

Solution nebulization inductively coupled plasma mass spectrometry (ICP-MS) was applied to the analysis of uranium isotope abundance ratios in individual particles. Particle screening was carried out before ICP-MS analysis using two different techniques: irradiation with thermal neutrons and fission track observation (so-called “fission track technique”) on the one hand and automated particle measurement (APM) in secondary ion mass spectrometry (SIMS) on the other hand. Uranium-bearing particles localized by the screening techniques were sampled individually by micro-sampling devices inside a scanning electron microscope and deposited on clean silicon wafers for subsequent chemical dissolution and ICP-MS measurement. The micro-sampling enables us to avoid polyatomic ion interferences and measure some uranium-bearing particles at the same time in isotopic analysis. Using both methods, particles from certified reference materials and a real-life sample taken at a nuclear facility were measured to evaluate the performance of the methods. Using ICP-MS combined with the fission track technique, the uranium isotope abundance ratios were successfully determined for individual particles with diameters ranging from 1.2 to 2.4 μm in a certified reference material (NBL CRM U100). The analysis of the real-life sample using ICP-MS combined with the fission track technique gave ²³⁵U/²³⁸U isotope abundance ratios between 0.0246 and 0.0376. When APM was used as the particle screening method for the real-life sample, ²³⁵U/²³⁸U isotope abundance ratios ranging from 0.0259 to 0.0432 were obtained. These values were higher than those obtained by a well-established method for particle analysis (SIMS). From these results, it can be concluded that both techniques allow selection and analysis of the uranium particles with the highest ²³⁵U abundance, which is the most important for nuclear safeguards.