Composition of uranium oxide particles related to TOF‐SIMS ion distributions

Abstract

Uranium oxide particles tens of micrometers in size, including natural and depleted UO 2 , U 3 O 8 , and UO 3 were analyzed using an IONTOF V time-of-flight secondary ion mass spectrometry (TOF-SIMS) V. Particulate samples were mounted on gold substrates made using a novel technique that reduced hydrocarbon contamination and volatile outgassing as well as provided an internal standard of Au x ion peaks to calibrate high masses. For UO 2 surfaces, the dominant U 3 O x and U 4 O y cations were U 3 O 6 + and U 4 O 8 + , whereas for both U 3 O 8 and UO 3 surfaces, they were U 3 O 7 + and U 4 O 9 +. Secondary ion abundance ratios contained additional information about the chemical composition of the sample related to the relative stability of the cluster ions. Relative stabilities of the most stable cation isomers corresponding to masses observed in SIMS spectra were calculated using high-level density functional theory in order to compare ion stabilities to TOF-SIMS intensity distributions. Cation isomers having high oxygen content were doublets, and those having low oxygen content were quartet spin states. Depth profile trends for 'protonation' ratio and 'lattice valence', as defined by Plog, Wiedmann, and Benninghoven, were used to distinguish U 3 O 8 from UO 3 . Cations containing a greater number of uranium atoms were also found to have a lower protonation ratio. UO 2 and U 3 O 8 surfaces show a steeper reduction in protonation ratio compared to UO 3 surfaces which exhibit a nearly constant near-surface protonation ratio followed by a more gradual smaller decline with depth. We interpret secondary ion distribution results using density functional quantum mechanics calculations comparing the relative stability of cations and anions for different oxygen atom environments.

Environmental modeling of uranium interstitial compositions of non-stoichiometric oxides: experimental and theoretical analysis

“…The environmental protection strategies for monitoring the migration processes of radionuclides in the geosphere and long storage of nuclear waste have involved complex models of environmental processes and experimental chemical, geochemical, physical and biological factors (Stoliker et al 2011;Ilton et al 2012;Jung et al 2012;Malaviya and Singh 2012;Chandrasekaran et al 2011;Sundararajan et al 2011;Mayer et al 2013;Walton and Mitchell 2013;Qiu and Burns 2013;Hocking et al 2013;Knope and Soderholm 2013). This complexity of the theoretical modeling and the experimental design of radionuclide migration in surface and groundwater; its speciation in wastewater, sorption onto soils, sediments and manure has been further complicated by the dual physical nature uranium between rare element and semiconductor as a result of the characteristics of 5f-electrons at an intermediate localization regime.…”

Recent Advances in Nuclear Forensic Chemistry

“…The use of LA-ICP-MS for this purpose has been discussed briefly, but secondary ion mass spectrometry (SIMS) is currently the most common technique for spatially resolved MS . SIMS enables concurrent determination of the shape, composition, and isotopic ratios present in a sample, indicating the homogeneity of a sample at relatively small scales (generally on the order of micrometers). ,− Ionization is achieved by focusing an ion beam onto the sample, causing secondary ions to be ejected. Since the sample is only ionized at its surface, minimal sample preparation is required for SIMS and imaging is also possible.…”

2013 Atomic spectrometry update—A review of advances in environmental analysis

“…The authors concluded that this enhanced method will be a valuable tool to assist in the certication of future RMs. It was possible 49 to distinguish between different valences states such as UO 2 , U 3 O 8 and UO 3 on surface layers and through depth proles of U-oxide particles by interrogating the ion distributions measured by TOF-SIMS.…”