A primary tool for detecting undeclared nuclear activities is the analysis of uranium-bearing particles collected on cotton swipes. For many years, secondary ion mass spectrometry (SIMS) has been used as one of the mainstay techniques for particle analysis of nuclear safeguards samples. SIMS is unique in that it is the only technique that can both localize the particles of interest and also provide the isotopic composition of single particles. This paper presents data obtained on standard uranium particle samples using large geometry (LG)-SIMS instruments equipped with the newly developed, automated particle measurement screening software. Both sample screening measurements and microbeam analyses on individual particles are presented. The enhanced performance of the SIMS method for nuclear safeguards applications using LG-SIMS instruments equipped with automated screening capabilities is also discussed. Figure 7. Microbeam measurements, (a) 234 U versus 235 U and (b) 236 U versus 235 U on particles selected from the screening measurement. Intersection of dotted lines indicates the nominal values for 234 U, 235 U, or 236 U atom % for SRM U005a and U010. Error bars correspond to AE 2s.Nuclear safeguards applications using LG-SIMS

Samples of cerium were exposed to hydrogen under controlled conditions causing cerium hydride sites to nucleate and grow on the surface. The hydriding rate was measured in situ, and the hydrides were characterised using secondary ion mass spectrometry, scanning electron microscopy, and optical microscopy. The results show that the hydriding rate proceeded more quickly than earlier studies. Characterisation confirmed that the hydrogen is confined to the sites. The morphology of the hydrides was confirmed to be oblate, and stressed material was observed surrounding the hydride, in a number of cases lathlike features were observed surrounding the hydride sites laterally with cracking in the surface oxide above them. It is proposed that during growth the increased lattice parameter of the CeH2 induces a lateral compressive stress around the hydride, which relieves by the ca. 16% volume collapse of the γ-Ce to α-Ce pressure induced phase transition. Cracking of the surface oxide above the laths reduces the diffusion barrier to hydrogen reaching the metal/oxide interface surrounding the hydride site and contributes to the anisotropic growth of the hydrides.

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