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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Metallothionein deficiency aggravates depleted uranium-induced nephrotoxicity

Depleted uranium (DU) has been widely used in both civilian and military activities, and the kidney is the main target organ of DU during acute high-dose exposures. In this study, the nephrotoxicity caused by DU in metallothionein-1/2-null mice (MT −/−) and corresponding wild-type (MT +/+) mice was investigated to determine any associations with MT. Each MT −/− or MT +/+ mouse was pretreated with a single dose of DU (10 mg/kg, intraperitoneal injection) or an equivalent volume of saline. After 4 days of DU administration, kidney changes were assessed. After DU exposure, serum creatinine and serum urea nitrogen in MT −/− mice significantly increased than in MT +/+ mice, with more severe kidney pathological damage. Moreover, catalase and superoxide dismutase (SOD) decreased, and generation of reactive oxygen species and malondialdehyde increased in MT −/− mice. The apoptosis rate in MT −/− mice significantly increased, with a significant increase in both Bax and caspase 3 and a decrease in Bcl-2. Furthermore, sodium-glucose cotransporter (SGLT) and sodium-phosphate cotransporter (NaPi-II) were significantly reduced after DU exposure, and the change of SGLT was more evident in MT −/− mice. Finally, exogenous MT was used to evaluate the correlation between kidney changes induced by DU and MT doses in MT −/− mice. The results showed that, the pathological damage and cell apoptosis decreased, and SOD and SGLT levels increased with increasing dose of MT. In conclusion, MT deficiency aggravated DU-induced nephrotoxicity, and the molecular mechanisms appeared to be related to the increased oxidative stress and apoptosis, and decreased SGLT expression. - Highlights: • MT −/− and MT +/+ mice were used to evaluate nephrotoxicity of DU. • Renal damage was more evident in the MT −/− mice after exposure to DU. • Exogenous MT also protects against DU-induced nephrotoxicity. • MT deficiency induced more ROS and apoptosis after exposure to DU. • MT deficiency down-regulated SGLT expression after exposure to DU.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Use of an ion mobility spectrometer for detecting uranium compounds

The safeguards community currently lacks a method to rapidly determine the chemical form of radioactive and non-radioactive compounds in real time during inspection activities. Chemical speciation identification can provide important information on both the types of materials that are collected during environmental sampling and can inform inspectors as to where to focus efforts during inspections or complementary access visits. Ion Mobility Spectrometry (IMS) is an established field technique for the detection of explosives, narcotics, and other organic compounds. More recently, electrospray ionization (ESI) has been used to introduce inorganic compounds to IMS instruments for analysis. These techniques have shown the ability to supply chemical information about the compounds being analyzed. Although these laboratory based instruments use a liquid-based injection system, there is evidence in the literature of unaltered and intact pharmaceutical tablets being volatilized and ionized in open atmosphere using heat and a Ni-63 source. Lastly, this work determined that a commercial-off-the-shelf (COTS) IMS could be used for the identification of solid uranium compounds directly after sampling using a COTS sample swipe.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Optimization of uranium and plutonium separations using TEVA and UTEVA cartridges for MC-ICP-MS analysis of environmental swipe samples

We report that the analysis of environmental swipe samples for ultra-trace uranium (U) and plutonium (Pu) determinations is essential in the nuclear safeguards community. While mass spectrometry techniques for U and Pu detection continually improve, established separation methods are seldom reevaluated. Currently, actinide separations within the forensics community predominantly employ either Eichrom TEVA® or UTEVA® resins. The direct optimization of U and Pu separations utilizing both resins has not been widely reported. Here, several methods were explored with goals of increasing analyte recovery, acquiring cleaner blanks, and improving the separation efficiency of ultra-trace levels of U and Pu from environmental swipe samples. Finally, the optimized separation methodology of U and Pu was examined using certified reference materials and archived environmental swipe samples.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2020

Bridging the Transuranics with Uranium(IV) Sulfate Aqueous Species and Solid Phases

Isolating isomorphic compounds of tetravalent actinides (i.e., Th IV , U IV , Np IV , and Pu IV ) improve our understanding of the bonding behavior across the series, in addition to their relationship with tetravalent transition metals (Zr and Hf) and lanthanides (Ce). Similarities between these tetravalent metals are particularly illuminated in their hydrolysis and condensation behavior in aqueous systems, leading to polynuclear clusters typified by the hexamer [M IV 6 O 4 (OH) 4 ] 12+ building block. Prior studies have shown the predominance and coexistence of smaller species for Th IV (monomers, dimers, and hexamers) and larger species for U IV , Np IV , and Pu IV (including 38-mers and 70-mers). We show here that aqueous uranium(IV) sulfate also displays behavior similar to that of Th IV (and Zr IV ) in its isolated solidphase and solution speciation. Two single-crystal X-ray structures are described: a dihydroxide-bridged dimer (U 2 ) formulated as U 2 (OH) 2 (SO 4 ) 3 (H 2 O) 4 and a monomer-linked hexamer framework (U-U 6 ) as (U(H 2 O) 3.5 ) 2 U 6 O 4 (OH) 4 (SO 4 ) 10 (H 2 O) 9 . These structures are similar to those previously described for ThIV. Moreover, cocrystallization of monomer and dimer and of dimer and monomer–hexamer phases for both Th IV (prior) and U IV (current) indicates the coexistence of these species in solution. Because it was not possible to effectively study the sulfate-rich solutions via X-ray scattering from which U 2 and U-U 6 crystallized, we provide a parallel solution speciation study in low sulfate conditions, as a function of the pH. Raman spectroscopy, UV–vis spectroscopy, and small-angle X-ray scattering of these show decreasing sulfate binding, increased hydrolysis, increased species size, and increased complexity, with increasing pH. Furthermore, this study describes a bridge across the first half the actinide series, highlighting U IV similarities to Th IV , in addition to the previously known similarities to the transuranic elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Synthesis of Trimethyltriazacyclohexane (Me 3 tach) Sandwich Complexes of Uranium, Neptunium, and Plutonium Triiodides: (Me 3 tach) 2 AnI 3

1,3,5-Trimethyl-1,3,5-triazacyclohexane (Me 3 tach) readily complexes uranium triiodide to form (Me 3 tach) 2 UI 3 . Further, the complex is soluble in THF and arenes and can function as a source of UI 3 to form organometallic U(III) complexes. When dissolved in pyridine (py), (Me3tach)2UI3 forms (Me 3 tach)UI 3 (py) 2 . A related complex with the larger 1,4,7-trimethyl-1,4,7-triazacyclononane (Me 3 tacn) ligand, namely (Me 3 tacn)UI 3 (THF), was synthesized for comparison. Since X-ray quality crystals of (Me 3 tach) 2 UI 3 can be synthesized in high yield even with small-scale reactions, the system is ideal for extension to transuranium elements. Accordingly, the neptunium and plutonium complexes (Me 3 tach) 2 NpI 3 and (Me 3 tach) 2 PuI 3 were synthesized in an analogous manner from NpI 3 (THF) 4 and PuI 3 (THF) 4 , respectively.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Linear versus Bent Uranium(II) Metallocenes—A Local Vibrational Mode Study

Uranium metallocenes have recently attracted attention driven by their use as catalysts in organometallic synthesis. In addition to bent U(IV) and U(III), an U(II) metallocene [(η 5 -C 5 i Pr 5 ) 2 U] was synthesized with an unusual linear Cp–U–Cp angle. Here, in this work, we investigated 22 U(II) metallocenes, (i) assessing the intrinsic strength of the U-ring interactions in these complexes with a novel bond strength measure based on our local vibrational mode analysis and (ii) systematically exploring what makes these U(II) metallocenes bent. We included relativistic effects through the NESCau Hamiltonian and complemented the local mode analysis with natural bonding orbital (NBO) and quantum theory of atoms in molecules (QTAIM) data. Our study led to the following results: (i) reduction of bulky U-ring ligand substituents does not lead to bent complexes for alkyl substituents ( i Pr and i Bu) in contrast to SiMe 3 ring substituents, which are all bent. (ii) The most bent complexes are [(η 5 -C 5 H 4 SiMe 3 ) 2 U] (130°) and [η 5 -P 5 H 5 ) 2 U] (143°). (iii) Linear complexes showed one hybridized NBO with s/d character, while bent structures were characterized by s/d/f mixing. (iv) We did not observe a correlation between the strength of the U-ring interaction and the amount of the ring-U-ring bend; the strongest interaction was found for [η 5 -Cp) 2 U] and the weakest for [η 5 -P 5 H 5 ) 2 U]. In conclusion, our results provide a foundation for the design of U(II) metallocenes with specific physicochemical properties and increased reactivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Mapping the Electronic Structure of the Uranium(VI) Dinitride Molecule, UN 2

A combined anion photoelectron spectroscopic and relativistic electronic-structure computational study of the electronic structure of the UN 2 molecule is reported. Since the photoelectron spectrum of uranium dinitride’s negative ion, UN 2 - , (UN 2 plus an additional electron) directly reflects the electronic structure of neutral UN 2 , we have measured and relied upon the photoelectron spectrum of the UN 2 – anion as a means of mapping the electronic structure of neutral UN 2 . In addition to the electron affinity of the UN 2 ground state (the energy released when attaching an electron to UN 2 molecule), energy levels of the UN 2 excited states (electronic states with higher energies than the ground state) were well characterized by the close interplay between experiment and high-level theory. We found that both electron attachment and electronic excitation significantly bend the UN 2 molecule and elongate its U≡N bond. Implications for the activation of UN 2 are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Electronic and Geometric Contributors to Hydrogen Binding in Uranium Oxide Grain Boundaries

Hydrogen induced corrosion of uranium, which leads to the formation of toxic and pyrophoric UH 3 , raises significant safety concerns for long-term storage of nuclear materials. Previous work suggests hydrogen diffuses through the grain boundaries (GBs) of the passivating oxide layer to initiate hydriding reactions. However, the atomistic mechanisms underlying this phenomenon and the structural factors that control its initiation are not well understood. To address this knowledge gap, here we use a high-throughput density functional theory (DFT) workflow to investigate the adsorption of H and H 2 in the defective bulk UO 2 . Specifically, we have exhaustively investigated the adsorption of H (107 sites) and H 2 (26 sites) in three different coincident site lattice (CSL) GBs: Σ3, Σ5, and Σ9. Compared to the binding energies in pristine UO 2 , we observe significantly stronger hydrogen adsorption at these GB sites. Interestingly, we find that the trends in H and H 2 adsorption vary considerably across the three GB models. In particular, while a small number of sites in Σ5 and Σ9 show exothermic adsorption of H and H 2 , respectively, no such sites are found in Σ3. These results provide fundamental atomistic insights that could guide the development of future corrosion mitigation strategies for the storage of nuclear materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

U–C Bond Insertion, Ring-Opening, and C–H Activation in a Uranium Bis(diisopropylamino)cyclopropenylidene (BAC) Adduct

Reaction of [U(NR 2 ) 3 ] (R = SiMe 3 ) with 1 equiv of bis(diisopropylamino)cyclopropenylidene (BAC) in Et 2 O results in the formation of [(NR 2 ) 3 U(BAC)] (1), which can be isolated in modest yields. Thermolysis of 1 in C 6 D 6 at 85 °C results in the formation of the ring-opened U(IV) product, [(NR 2 ) 2 U{N(R)(SiMe 2 CH=C(NiPr 2 )C(NiPr 2 )=CH)}] (2), which can be isolated in low yields. Mechanistic studies suggest that the formation of 2 proceeds via dissociation of BAC from 1 to regenerate [U(NR 2 ) 3 ], which converts into [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] at the elevated temperatures. BAC then inserts into the U–C bond of [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] to generate a cyclopropenyl intermediate, which undergoes ring opening and C–H activation to afford the final product, 2. We hypothesize that the ring-opening generates an unobserved carbene intermediate. Notably, thermolysis of a 1:1 mixture of independently prepared [U{N(R)(SiMe 2 CH 2 )}(NR 2 ) 2 ] and BAC results in clean formation of 2, providing strong support for the proposed mechanism. The formulations of both 1 and 2 were confirmed by X-ray crystallography. Finally, theoretical calculations indicate that the hypothesized uranium carbene intermediate features strong U–C bonding, potentially with some carbyne character in the electronic structure.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

Catalytic Dehydrogenation of Dimethylamine Borane by Highly Active Thorium and Uranium Metallocene Complexes

In the thorium and uranium complexes (C 5 Me 5 ) 2 AnMe 2 , [(C 5 Me 5 ) 2 An(H)(μ-H)] 2 (An = Th, U) and [(C 5 Me 5 ) 2 U(H)] 2 dehydrogenate dimethylamine borane (Me2NH·BH3) at room temperature. Upon mild heating at 45 °C, turnover frequencies (TOFs) of 400 h –1 are obtained, which is comparable to some of the fastest Me 2 NH·BH 3 dehydrogenation catalysts known in the literature. We propose a β-hydride elimination mechanism for dehydrogenation because of the observation of Me 2 N=BH 2 , Me 2 N=BMe 2 , and Me 2 N=BHMe in the 11 B NMR spectra of catalytic and stoichiometric reactions. The similar catalytic metrics between the actinide dimethyl and hydride complexes with Me 2 NH·BH 3 indicate that the actinide hydride complexes are the active catalysts in this chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Pentavalent Uranium Enriched Mineral Surface under Electrochemically Controlled Reducing Environments

Redox reactions of uranium (U) in aqueous environments have important impacts on the mobility and isotopic fractionation of U in the geosphere. Pentavalent U as the cationic uranyl ion, UO 2 +, is rarely observed in naturally occurring samples because of its limited lifetime, but it may be an important intermediate state controlling the redox kinetics between hexavalent and tetravalent U. Increasing evidence has indicated that U(V) can be stabilized under laboratory conditions. Here, we showed that U(V) is the dominant species on the magnetite (Fe 3 O 4 ) surface under reducing conditions controlled by electrochemical methods. Cyclic voltammetry reveals coupled redox peaks corresponding to the U(VI)O 2 2+ /U(V)O 2+ one-electron redox reaction. Magnetite electrodes polarized at a series of potentials to reduce U(VI)O 2 2+ were characterized by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and Auger electron mapping. Overall, the results showed that up to twice the amount of U(V) to U(VI) was present on the magnetite surface. U(V) adopted a typical uranyl-type structure, and the U coverage on the magnetite surface increased with decreasing potentials. The formation of mixed-valence U(V)/U(VI) species on the surface of magnetite may hinder the U(V) disproportionation reaction, thereby eliminating the presence of tetravalent U. These results show that U(V) can exist over short time scales as the dominant U species on mineral surfaces under selected reducing conditions by the controlled polarization of a mineral electrode.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Spectroscopic and Computational Evidence of Uranium Dihydrogen Complexes

Dihydrogen complexation, a phenomenon with robust precedent in the transition metal series, is spectroscopically detected for a uranium(III) complex and thereby extended for the first time to the 5f series. The vacant coordination site and low valence of (C 5 H 4 SiMe 3 ) 3 U prove to be key to the reversible formation of (C 5 H 4 SiMe 3 ) 3 U–H 2 (complex 1), and the paramagnetism of the f 3 center facilitates the detection of complex 1 by NMR spectroscopy. Density functional theory calculations reveal that the delocalization of the 5f electron density from (C 5 H 4 SiMe 3 ) 3 U onto the side-on dihydrogen ligand is crucial to complex formation, an unusual bonding situation for an actinide acid–base complex. Here, the spectroscopic and computational results are compared to those reported for lanthanide metallocenes to yield insight into the nature of–and future possibilities for–f-element dihydrogen complexation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Piezomagnetism and magnetoelastic memory in uranium dioxide

Uranium dioxide (UO 2 ) is a prime nuclear fuel and perhaps the most thoroughly studied actinide material to date. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. The magnetic state of this cubic material is characterized by a non- collinear antiferromagnetic structure and multidomain Jahn-Teller distortions that could be behind novel thermal properties. Here we show that single crystals of UO 2 , subjected to magnetic fields up to 95 T in the magnetic state, exhibit the abrupt appearance of positive linear magnetostriction leading to a trigonal distortion. Upon reversal of the field the linear term also reverses sign, a hallmark of piezomagnetism. The switching phenomenon occurs at ± 18 T and persists during subsequent field reversals, demonstrating robust magneto-elastic memory. This is the first example of piezomagnetism in an actinide spin system and the magneto-elastic memory loop here is nearly an order of magnitude wider in field than those previously observed, making UO 2 the hardest piezomagnet known. The possibility of an inverse phase with reduced magnetocrystalline anisotropy is considered to explain these effects.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A microfluidic electrochemical cell for studying the corrosion of uranium dioxide (UO 2 )

We have developed a specialized microfluidic electrochemical cell that enables in situ investigation of the electrochemical corrosion of microgram quantities of redox active solids. The advantage of downscaling is the reduction of hazards, waste, expense, and greatly expanding data collection for hazardous materials, including radioactive samples. Cyclic voltammetry was used to monitor the oxidation–reduction cycle of minute quantities of micron-size uraninite (UO 2 ) particles, from the formation of hexavalent uranium (U(VI)), U 3 O 7 and reduction to UO 2+x . Reaction progress was also studied in situ with scanning electron microscopy. The electrochemical measurements matched those obtained at the bulk-scale and were consistent with ex situ characterization of the run products by X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and atomic force microscopy; thus, demonstrating the utility of the microfluidic approach for studying radioactive materials.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2014

Atomistic study of porosity impact on phonon driven thermal conductivity: Application to uranium dioxide

We present here an analytical method, based on the kinetic theory, to determine the impact of defects such as cavities on the thermal conductivity of a solid. This approach, which explicitly takes into account the effects of internal pore surfaces, will be referred to as the Phonon Interface THermal cONductivity (PITHON) model. Once exposed in the general case, this method is then illustrated in the case of uranium dioxide. It appears that taking properly into account these interface effects significantly modifies the temperature and porosity dependence of thermal conductivity with respect to that issued from either micromechanical models or more recent approaches, in particular, for small cavity sizes. More precisely, it is found that if the mean free path appears to have a major effect in this system in the temperature and porosity distribution range of interest, the variation of the specific heat at the surface of the cavity is predicted to be essential at very low temperature and small sizes for sufficiently large porosity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Ab initio study of pressure induced structural and electronic properties in uranium monobismuthide

We have investigated the pressure induced structural and electronic properties of uranium monobismuthide. The total energy as a function of volume is obtained by means of self-consistent tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). We predict structural phase transition from NaCl to CsCl-type structure at a pressure of 4.6 GPa. From energy band diagram it is observed that UBi exhibits metallic behavior. The calculated equilibrium lattice parameter is in good agreement with the experimental and other theoretical work.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Persistence of uranium emission in laser-produced plasmas

Detection of uranium and other nuclear materials is of the utmost importance for nuclear safeguards and security. Optical emission spectroscopy of laser-ablated U plasmas has been presented as a stand-off, portable analytical method that can yield accurate qualitative and quantitative elemental analysis of a variety of samples. In this study, optimal laser ablation and ambient conditions are explored, as well as the spatio-temporal evolution of the plasma for spectral analysis of excited U species in a glass matrix. Various Ar pressures were explored to investigate the role that plasma collisional effects and confinement have on spectral line emission enhancement and persistence. The plasma-ambient gas interaction was also investigated using spatially resolved spectra and optical time-of-flight measurements. The results indicate that ambient conditions play a very important role in spectral emission intensity as well as the persistence of excited neutral U emission lines, influencing the appropriate spectral acquisition conditions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Stark and Zeeman effect in the [18.6]3.5 – X(1)4.5 transition of uranium monofluoride, UF

High resolution spectra of the 0-0 band of the [18.6]3.5 – X(1)4.5 transition of uranium monofluoride, UF, obtained using a laser ablation spectrometer, showed a perturbation in the upper state. Examination of the Stark and Zeeman effects yielded permanent electric dipole moments of 2.01 and 1.88 D and magnetic g-factors of 3.28 and 3.26 for the ground and excited states, respectively. Both the dipole moment and g-factor of the ground state are in good agreement with ab initio calculations [I. O. Antonov and M. C. Heaven, J. Phys. Chem. A 117, 9684 (2013)]. The Zeeman effect results confirm that the ground state arises primarily from the U{sup +}(5f {sup 3}7s{sup 24}I{sub 4.5})F{sup −} configuration and suggest several possible configurations for the upper state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗