LG-SIMS oxygen isotope and impurity distribution characterization of U-O-bearing particles as signatures of process history

Oxygen isotopes and impurities may provide nuclear forensic signatures related to processing of uranium materials. These signatures can be evaluated by secondary ion mass spectrometry (SIMS). Here we describe such SIMS characterization of U-O-bearing materials and discuss the need for reference materials to understand signatures from real materials. SIMS oxygen isotope characterization: The various chemical reactions for converting uranium ore concentrates (UOCs) to desired species (e.g. UO2, U3O8, etc.) can fractionate oxygen isotopes in potentially distinguishable ways. Oxygen from the local environment may also impart their isotope signatures during processing. Bulk analysis of U-O-bearing materials can provide 18O/16O ratios with a high-level of precision for evaluating process histories. SIMS can complement bulk oxygen isotope data by providing additional signatures related to isotope homogeneity at micron-level scales (e.g. particles from swipes, small fragments of fuel pellets). The isotope homogeneity or heterogeneity of a material may be related to (1) equilibrium kinetics specific to processing reactions and/or (2) the presence or lack of multiple endmember oxygen isotope sources. Figure 1 shows example SIMS particle data from New Brunswick Laboratory certified reference material (CRM) 129-A (U3O8) and two UOCs, one consisting of U3O8 and one consisting of uranyl peroxide (we note the instrument was calibrated to produce a mean δ18O value of 0‰ for CRM 129-A). Here, the two U3O8 samples have resolvable mean δ18O values, and the uranyl peroxide sample has a lower particle-to-particle variability when compared to the U3O8 sample datasets. These characteristics likely reflect the specific process histories of each material.