Dual-field multicollector LG-SIMS analysis of mixed U–Pu reference particles

Abstract

In this study, we demonstrate a new dual-field multicollector protocol for magnetic sector large-geometry secondary ion mass spectrometry (LG-SIMS) that enables concurrent analysis of U and Pu isotopes. We apply this analysis protocol to recently produced mixed U–Pu microparticle reference materials, called UPu-100A. These particles, loaded on a Si substrate, show highly reproducible U and Pu isotopic and U/Pu assay results, with particle-to-particle molar variability typically less than 1% relative, and down to 0.1% for ²³⁵U/²³⁸U and less than 0.3% for ²⁴⁰Pu/²³⁹Pu. We demonstrate the impact of surface and primary beam sputter chemistry on the acquisition and interpretation of mixed-actinide particle analyses. We show that, in general, consuming most of each particle within a single analysis yields the most reproducible results. Using O₃⁻ primary ions reduces sputter chemistry artifacts during particle depth profiling on Si relative to O⁻ primary ions, which further enhances reproducibility. The Pu/U relative sensitivity factors for O₃⁻ and O⁻ primary ions on Si were 2.036 ± 0.016 (1 standard deviation, SD) and 2.142 ± 0.034 (1 SD), respectively. This work highlights how integration of novel analytical protocols and fit-for-purpose reference materials can push the boundaries of particle-scale material characterization.