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An automated microextraction method coupled to an inductively coupled plasma - mass spectrometer (ICP-MS) was developed for the direct analysis of solid uranium particulates on the surface of cotton swipes. The microextraction probe extracts particulates from the sample surface, in a flowing solvent, and directs the removed analyte to an ICP-MS for isotopic determination. The automated system utilizes a mechanical XY stage that is software controlled with the capability of saving and returning to specific locations and a camera focused to the swipe surface for optimal viewing of the extracted locations (

We investigate the sputtering and ionization process that takes place during secondary ion mass spectrometry (SIMS) analysis in order to develop a better understanding of the underlying controls on elemental and molecular oxide secondary ion yields. Using data from a suite of uranium compounds that were sputtered with an O- primary beam on a NanoSIMS 50L, our goal is to understand whether a compound’s intrinsic properties, or processes operating at the sputtering site, exert the greatest influence over the relative abundances of uranium elemental and molecular oxide secondary ions observed during an analysis. While the observed 238U/238U16O and 238U/238U16O2 of the various compounds exhibit considerable overlap, there are relationships between the weighted mean 238U/238U16O and 238U/238U16O2 ratios for the various compounds and their enthalpies of formation. This reinforces the existing theory that the nature of the material being sputtered can influence relative ion yields (e.g. the SIMS matrix effect), but we also document significant evidence for the influence of processes operating at the sputtering site as a major factor. The existence of a strong relationship between the relative uranium molecular oxide production rate and the mass fractionation regimes taking place within an analysis, as well as the existence of sudden shifts in molecular oxide production rates taking place within an analysis, provide further evidence for the importance of processes related to the sputtering and ionization dynamics as exerting the most control over observed ion yields. Evaluation of our data within the context of existing models for secondary ion production during SIMS analysis highlights the need for additional models that consider the competing influences of a sample’s chemical and/or structural form, reactions taking place at the sputtering site, as well as the ionization and ion extraction dynamics of the various elemental and molecular oxide species.

Self-charging of radioactive uranium oxide particles was measured by comparing the electrostatic surface-charge characteristics of the uranium particles to various airborne dust particulates. Though radioactive aerosols can gain charge through various decay mechanisms, researchers have traditionally assumed that the radioactive aerosols do not carry any additional charge relative to other atmospheric dust particles as a consequence of charge neutralization over time. In this work, we evaluate this assumption by directly examining the surface charge and charge density on airborne uranium oxide particles and then comparing those characteristics with charging of other natural and engineered airborne dust particles. Based on electric field–assisted particle levitation in air, the surface charge, charge distribution as a function of particle size, and surface charge density were determined for uranium oxide aerosols (

A NanoSIMS 50L is used to investigate uranium molecular (235U16O, 236U16O, 238U16O, 235U1H, 238U1H, 236U16O1H, and 238U16O1H) and elemental (235U, 236U, and 238U) secondary ion production during sputtering of synthetic UO2 and the NIST-610 standard to determine if: (1) the 236U16O/238U16O molecular oxide ratio performs better than the 236U/238U elemental ratio, and (2) there is co-variance between the molecular hydrides and oxides. Despite an order of magnitude greater abundance of 236U16O secondary ions (compared to 236U), the 236U16O/238U16O ratios are less accurate than the 236U/238U ratios. Further work is needed before the higher count rate of the 236U16O secondary ion can be used to obtain a better 236U/238U ratio. The second objective was undertaken because correction for the interference of 235U1H on the 236U secondary ion species typically utilizes the 238U1H/238U ratio. This becomes problematic in samples containing 239Pu, so our aim was to understand if the hydride formation rate can be constrained independently of having to measure the 238U1H. We document correlations between the hydride (238U1H and 238U16O1H) and oxide (236U16O) secondary ions, suggesting that pursuing an alternative correction regime is worthwhile.

Direct isotope ratio analysis of solid uranium particulates on cotton swipes was achieved using a solution-based microextraction technique, coupled to a quadrupole inductively coupled plasma - mass spectrometer (ICP-MS). This microextraction-ICP-MS methodology provides rapid isotopic analysis which could be applicable to nuclear safeguards measurements. Particulates of uranyl nitrate hexahydrate (UO

A cation exchange chromatography method employing sulfonated polysterene cation resin (DOWEX AG50-X8) was developed in order to separate rare-earth elements (REEs) from uranium-rich materials. The chemical separation scheme is designed to reduce matrix effects and consequently yield enhanced ionization efficiencies for concentration determinations of REEs without significant fractionation using solution mode-inductively coupled plasma mass spectrometry (ICP-MS) analysis. The method was applied to determine REE abundances in four uraninite (ideally UO2) samples and their associated U(VI) alteration minerals. In three of the samples analyzed, the concentration of REEs for primary uraninite are higher than those for their corresponding secondary uranium alteration phases. The results for U(VI) alteration minerals of two samples indicate enrichment of the light REEs (LREEs) over the heavy REEs (HREEs). This differential mobilization is attributed to differences in the mineralogical composition of the U(VI) alteration. There is a lack of fractionation of the LREEs in the uraninite alteration rind that is composed of U(VI) minerals containing Ca2+ as the interlayer cation (uranophane and bequerelite); contrarily, U(VI) alteration minerals containing K+ and Pb2+ as interlayer cations (fourmarierite, dumontite) indicate fractionation (enrichment) of the LREEs. Our results have implications for nuclear forensic analyses since a comparison is reported between the REE abundances for the CUP-2 (processed uranium ore) certified reference material and previously determined values for uranium ore concentrate (UOC) produced from the same U deposit (Blind River/Elliott Lake, Canada). UOCs represent the most common form of interdicted nuclear material and consequently is material frequently targeted for forensic analysis. The comparison reveals similar chondrite normalized REE signatures but variable absolute abundances. Based on the results reported here, the latter may be attributed to the differing REE abundances between primary ore and associated alteration phases, and/or is related to varying fabrication processes adopted during production of UOC.

Identifying the provenance of uranium-rich materials is a critical objective of nuclear forensic analysis. Rare earth element (REE) distributions within uranium ores are well-established forensic indicators, but quantifying and correlating trace element signatures for U ores to known deposits has thus far involved intricate statistical analyses. This study reports average chondrite normalized (CN)-REE signatures for important U deposit types worldwide, which are then employed to evaluate U ore paragenesis using a simple linear regression analysis. This technique provides a straightforward method that can aid in determining the deposit type of U ores based on their REE abundances, and combined with other forensic indicators (e.g. radiogenic isotope signatures) can provide essential provenance information for nuclear materials.

Understanding the crystal chemistry, materials properties, and thermodynamics of uranyl minerals and their synthetic analogs is an essential step for predicting and controlling the long-term environmental behavior of uranium. Uranyl vanadate minerals are relatively insoluble and widely disseminated within U ore deposits and mine and mill tailings. Pure uranyl vanadate mineral analogs were synthesized for investigation using high-temperature drop solution calorimetry. Calculated standard-state enthalpies of formation were found to be −4928.52 ± 13.90, −5748.81 ± 13.59, and −6402.88 ± 21.01, kJ/mol for carnotite, curienite, and francevillite, respectively. Enthalpies of formation from binary oxides for uranyl vanadate minerals exhibit a positive linear correlation as a function of the acidity of oxides. Normalized charge deficiency per anion (NCDA) is presented to relate bonding requirements of the structural units and interstitial complexes. An exponential correlation was observed between NCDA and energetic stability (enthalpy of formation from binary oxides) for the studied minerals. Additionally, NCDA and oxide acidity exhibit an exponential correlation where decreasing oxide acidity results in an exponential decrease in NCDA. The number of occurrences of uranyl vanadate mineral species are found to correlate with both enthalpy of formation from oxides and NCDA.

This study reports major, minor, and trace element data and Sr isotope ratios for 11 uranium ore (uraninite, UO 2+x ) samples and one processed uranium ore concentrate (UOC) from various U.S. deposits. The uraninite investigated represent ores formed via different modes of mineralization (e.g., high- and low-temperature) and within various geological contexts, which include magmatic pegmatites, metamorphic rocks, sandstone-hosted, and roll front deposits. In situ trace element data obtained by laser ablation-ICP-MS and bulk sample Sr isotopic ratios for uraninite samples investigated here indicate distinct signatures that are highly dependent on the mode of mineralization and host rock geology. Relative to their high-temperature counterparts, low-temperature uranium ores record high U/Th ratios (>1000), low total rare earth element (REE) abundances ( 300 ppm) of first row transition metals (Sc, Ti, V, Cr, Mn, Co, Ni), and radiogenic 87 Sr/ 86 Sr ratios (>0.7200). Comparison of chondrite normalized REE patterns between uraninite and corresponding processed UOC from the same locality indicates identical patterns at different absolute concentrations. This result ultimately confirms the importance of establishing geochemical signatures of raw, uranium ore materials for attribution purposes in the forensic analysis of intercepted nuclear materials.

Under humid conditions, uranyl fluoride ([(UO2F2)(H2O)]7·4H2O) undergoes a loss of fluorine to form a uranyl hydroxide species, which can be further hydrated to form a uranyl peroxide species. X-ray diffraction data of the uranyl peroxide product is presented for the first time. In addition, the temperature and humidity conditions under which these reactions occur have been clarified by a 220-day experiment using microRaman spectroscopy to track chemical changes in individual particles of uranyl fluoride. At 25 and 35∘C, uranyl fluoride is found to be stable at 32% relative humidity but not stable at and above 59% relative humidity. We show that water vapor pressure is the driving factor in formation of both the hydroxide and peroxide products. The kinetics of the transformation from uranyl fluoride into uranyl hydroxide is consistent with a denucleation reaction following the absorption of water molecules.

Uranium oxides are readily amenable to investigation using Raman spectroscopy, and this technique is frequently used as a chemical analysis tool. We show, in triuranium octoxide (U3O8), the presence of previously unreported Raman peaks located below 100 cm−1. By maximum intensity, the strongest peak in U3O8 appears at 54 cm−1 and is resolution limited, making this mode an ideal candidate for chemically identifying U3O8 using Raman spectroscopy. Detailed peak analysis indicates that the main spectral feature between 300 and 500 cm−1 is more accurately described by a septet than a triplet. Two samples of differing oxygen content show only minor differences in bulk crystal structure, but subtle changes in lattice dynamics are suggestive of defect scattering in analogy to UO2+x.

The chemical and isotopic (U, Pb, Sr) signatures for a suite (n = 23) of pristine (&gt, 80 wt. % UO2) and altered uraninite samples (&gt, 70&ndash, 80 wt. % UO2) from various locations worldwide have been determined for the purpose of identifying potential fingerprints for nuclear forensic analysis. The characterization of the uraninite samples included determination of major, minor and trace element contents, Sr, Pb, and U isotopic compositions, and secondary mineral assemblages. Due to the multivariate approach adopted in this study, principal component analysis (PCA) has been employed to allow the direct comparison of multiple variable types. The PCA results indicate that the geological origin (sandstone, metamorphite, intrusive, granite and unconformity) of pristine uraninite can be readily identified utilizing various combinations of major and/or trace element concentrations with isotopic compositions.