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.