Hydrothermal synthesis of homogenous and size-controlled uranium-thorium oxide micro-particles for nuclear safeguards

Particle analysis is one of the key-techniques used in field nuclear safeguards. Beyond traditional uranium isotopy measurement, other methodologies are implemented to better characterize materials. Among them, age dating at particle scale enables determine time elapsed since last chemical step separation/purification or enrichment. The 230Th-234U couple being most common radiochronometer, there a need for morphology and size controlled uranium-thorium mixed oxides particles that could be as reference materials during isotopic measurements. With this aim, oxide microspheres were synthesized using wet chemistry route. hydrothermal conversion aspartate precursors T = 433 K led dioxide micro-particles with spherical size, up 5 mol% thorium. In order remove impurities, densify micro-particles, control form final compounds, heat treatments performed under various atmospheres. Nearly stoichiometric (U,Th)O2 dioxides obtained reducing conditions (Ar-4%H2) while U3O8-based samples formed air, thorium incorporated structure 2 mol%. Last, homogeneity cation distribution was evaluated by methods, including PERALS α-scintillation counting, well X-EDS LG-SIMS analyzes individual particles, leading consistent results. Particularly, relative external reproducibility (2σ) 232Th+/238U+ ion ratios measured remained below 10%, paving way use these