Focused ion beam for improved spatially-resolved mass spectrometry and analysis of radioactive materials for uranium isotopic analysis
Dallas D. Reilly, Chelsie L. Beck, Edgar C. Buck, John Cliff, Andrew M. Duffin, Timothy G. Lach, Martin Liezers, Kellen Springer, Stephanie J. Tedrow, Mindy M. Zimmer
Abstract
The ability to acquire high-quality spatially-resolved mass spectrometry data is sought in many fields of study, but it often comes with high cost of instrumentation and a high level of expertise required. In addition, techniques highly regarded for isotopic analysis applications such as thermal ionization mass spectrometry (TIMS) do not have the ability to acquire spatially-resolved data. Another drawback is that for radioactive materials, which are often of interest for isotopic analysis in geochemistry and nuclear forensics applications, high-end instruments often have restrictions on radioactivity and non-dispersibility requirements. We have applied the use of a traditional microanalysis tool, the focused ion beam/scanning electron microscope (FIB/SEM), for preparation of radioactive materials either for direct analysis by spatially-resolved instruments such as secondary ion mass spectrometry (SIMS) and laser ablation inductively-coupled mass spectrometry (LA-ICP-MS), or similarly to provide some level of spatial resolution to techniques that do not inherently have that ability such as TIMS or quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS). We applied this preparation technique to various uranium compounds, which was especially useful for reducing sample sizes and ensuring non-dispersibility to allow for entry into non-radiological or ultra-trace facilities. Our results show how this site-specific preparation can provide spatial context for nominally bulk techniques such as TIMS and Q-ICP-MS. In addition, the analysis of samples extracted from a uranium dioxide fuel pellet via all methods, but especially NanoSIMS and LA-ICP-MS, showed enrichment heterogeneities that are important for nuclear forensics and are of interest for fuel performance.