New Particle Working Standards for NWAL Particle Laboratory Calibration and Quality Control
– LANL LG-SIMS Characterization and Evaluation

The LG-SIMS capability at Los Alamos National Laboratory (LANL) has a key role in evaluating the isotopic characteristics of particle materials generated by Savannah River National Laboratory (SRNL) and by Pacific Northwest Laboratory (PNNL) for the network of analytical laboratories (NWAL). Regarding the generation of new uranium working reference materials, the IAEA has provided specific isotope metrics that must be met in order for a material to be deemed a qualified working reference material. These metrics include (1) that materials must be isotopically homogeneous from particle to particle, with a limited number of outliers (evaluated via LG-SIMS isotope mapping of large particle populations); and (2) that LG-SIMS mean isotope compositions of particle datasets agree with bulk values determined by TIMS or MC-ICP-MS, and also agree with the compositions requested by the IAEA (which is evaluated by LG-SIMS high-precision single particle isotope analyses). For such evaluations the LANL LG-SIMS team has developed a counting statistics-based model that is used to determine the homogeneity (or lack thereof) of particle datasets, and can also be used to predict the level of analytical precision required to resolve two different endmember isotope compositions. Regarding the generation of working reference particles with mixed U and Pu, the LANL LG-SIMS team has been developing methods for their characterization, including techniques to minimize molecular hydride interferences, and evaluating intra-element and inter-element isotope homogeneity (or lack thereof) of particle materials. Challenges of producing mixed actinide working reference materials are discussed within the context of observed LG-SIMS isotope characteristics of mixed Pu-U test materials.