Uranium Ion Yields from Monodisperse Uranium Oxide Particles
Nicholas E. Sharp, John D. Fassett, David S. Simons
Secondary ion mass spectrometry (SIMS) plays an important role in nuclear forensics through its ability to identify isotopic ratios of particles accurately and precisely from samples obtained by inspectors . As the particle mass can be on the order of sub-picograms, it is important to maximize the sample utilization efficiency of U+ to make high-quality isotopic measurements. The influence of primary ion beam species and polarity on U+ sample utilization efficiency has been previously investigated by Ranebo et al. . However, the effect of sample substrate on uranium ion production efficiency and sputtering profile has not been investigated. This work will explore those influences on sample utilization efficiency by analyzing mono-disperse uranium oxide microspheres deposited onto graphite and silicon planchets. The particles were mapped using an automated scanning electron microscope and their coordinates were converted to the SIMS coordinate system using fiducial marks. Results indicate higher U+ sample utilization efficiencies when sputtering with O- and O2- on graphite planchets compared with O2+, whereas O2- gave higher U+ sample utilization efficiencies with silicon wafers compared to O- and O2+. Additionally, during sputtering of uranium particles on silicon wafers with O- and O2 , a sudden drop in U+ signal intensity was observed which was not present during sputtering with O2+ or any primary ion species for particles on graphite. This drop in U+ signal intensity occurred simultaneously with an increase in UO+ and UO2+ signals, indicating a change in the local matrix around the uranium particle that is unique to silicon compared to graphite.
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Uranium Ion Yields from Monodisperse Uranium Oxide Particles, Journal of Vacuum Science and Technology B, [online], https://doi.org/10.1116/1.4942612, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=919825
(Accessed December 3, 2023)