Direct, uncorrected, molecule-free analysis of 236U from uranium-bearing particles with NAUTILUS: a new kind of mass spectrometer

Abstract

We demonstrate use of the Naval Ultra-Trace Isotope Laboratory's Universal Spectrometer (NAUTILUS) at the U.S. Naval Research Laboratory (NRL) to measure ²³⁶U directly from uranium-bearing particles free from molecular isobaric interferences. Particles with ²³⁵U enrichments in the range of 0.32% to 3.28% and ²³⁶U enrichments from no enrichment to 0.015% provided by the International Atomic Energy Agency (IAEA) were analyzed directly using the NAUTILUS. We report the experimental data here without correcting for molecular hydrides and/or applying any other background subtractions. The results from all samples agreed with the certified values within standard error save for the ²³⁶U composition of the IRMM 023, which suffered from a combination of insufficient particle sizes and sub-μmol mol^{−1 236}U concentrations. We were able, however, to directly measure as low as three μmol mol⁻¹ of ²³⁶U in individual particles regardless of the ²³⁵U concentration. Our results are comparable with Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS) and serve as baseline for a more comprehensive comparison between LG-SIMS and the NAUTILUS in the future. Moreover, we demonstrate the ability of the NAUTILUS to generate raster ion images with the same ease as traditional LG-SIMS instruments. By combining our ability to measure ²³⁶U directly with raster ion imaging, we were able to detect a low intensity, small uranium-bearing particle in the presence of high molecular backgrounds for a non-ideal sample. This discovery could lead to more targeted and, therefore, less time intensive particle screening methodologies.