Temperature Dependence of Nuclear Quadrupole Resonance and the Observation of Metal-Ligand Covalency in Actinide Complexes: Cl in CsUOCl.

We report a study of the temperature dependence of Cl nuclear quadrupole resonance (NQR) transition energies and spin-lattice relaxation times () for U-depleted dicesium uranyl tetrachloride (CsUOCl) aimed at elucidating electronic interactions between the uranium center and atoms in the equatorial plane of the UO ion. The transition frequency decreases slowly with temperature below 75 K and with a more rapid linear dependence above this temperature. The spin-lattice relaxation time becomes shorter with temperature, and as temperatures increase, the decrease becomes nearly quadratic.

Equatorial Electronic Structure in the Uranyl Ion: CsUOCl and CsUOBr.

Electric field gradient (EFG) tensors in the equatorial plane of the linear UO ion have been measured by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments and computed by relativistic Kohn-Sham methods with and without environment embedding for CsUOCl and CsUOBr. This approach expands the possibilities for probing the electronic structure in uranyl complexes beyond the strongly covalent U-O bonds. The combined analyses find that one of the two largest principal EFG tensor components at the halogen sites points along the U-X bond (X = Cl, Br), and the second is parallel to the UO ion; in CsUOCl, the components are nearly equal in magnitude, whereas in CsUOBr, due to short-range bromide-cesium interactions, the equatorial component is dominant for one pair of Br sites and the axial component is larger for the second pair.

Measurement of local magnetic fields in actinide tetrafluorides.

Fluorine-19 magnetic shielding tensors have been measured in a series of actinide tetrafluorides (AnF) by solid state nuclear magnetic resonance spectroscopy. Tetravalent actinide centers with 0-8 valence electrons can form tetrafluorides with the same monoclinic structure type, making these compounds an attractive choice for a systematic study of the variation in the electronic structure across the 5f row of the Periodic Table. Pronounced deviations from predictions based on localized valence electron models have been detected by these experiments, which suggests that this approach may be used as a quantitative probe of electronic correlations.

Gas-phase molybdenum-99 separation from uranium dioxide by fluoride volatility using nitrogen trifluoride.

Production of the important Tc medical isotope parent, molybdenum-99 (Mo), the fissioning of high- and low-enriched uranium (HEU/LEU) targets followed by target dissolution in acid and solution-phase purification of Mo is time-consuming, generates quantities of corrosive radioactive waste, and can result in the release of an array of radionuclides to the atmosphere. An alternative Mo purification method has been devised that has the potential to alleviate many of these issues. Herein, we demonstrate the feasibility of a rapid Mo/Tc gas-phase separation from UO.

Properties of Pertechnic Acid.

Dilute aqueous pertechnic acid has long been known as strong monoprotic acid that behaves as a simple pertechnetate ion in aqueous solution. As pertechnic acid concentrates by evaporation, it becomes yellow and then dark red, and dark-red crystalline material may ultimately be obtained. We show that as pertechnic acid concentrates, at least three compounds are formed: a yellow viscous liquid, a colorless (not red) crystalline solid, and a small amount of an intensely colored red-purple compound.

Chemical and Isotopic Characterization of Noble Metal Phase from Commercial UO Fuel.

We report elemental and isotopic analysis for the noble metal fission product phase found in irradiated nuclear fuel. The noble metal phase was isolated from three commercial irradiated UO fuels by chemically dissolving the UO fuel matrix, leaving the noble metal phase as the undissolved residue. Macro amounts of this residue were dissolved using a KOH + KNO fusion and then chemically separated into individual elements for analysis by mass spectrometry.

In Situ Spectroscopic Analysis and Quantification of [Tc(CO)] in Hanford Tank Waste.

The quantitative conversion of nonpertechnetate [Tc(CO)] species in nuclear waste storage tank 241-AN-102 at the Hanford Site is demonstrated. A waste sample containing the [Tc(CO)] species is added to a developer solution that rapidly converts the nonemissive species into a luminescent complex, which is detected spectroscopically. This method was first demonstrated using a [Tc(CO)] sample of nonwaste containing matrix to determine a detection limit (LOD), resulting in a [Tc(CO)] LOD of 2.

Monitoring bromide effect on radiolytic yields using observations of uranyl oxide precipitation in the electron microscope.

During electron microscopy observations of uranium-bearing phases and solutions in a liquid cell, the electron beam induced radiolysis causes changes in the chemistry of the system. This could be useful for investigating accelerated alteration of UO and can be also used to monitor radiolytic effects. Low concentrations of bromide in aqueous solutions are known to reduce the generation rate of HO during radiolysis and increase H production.

Chemical Trends in Solid Alkali Pertechnetates.

Insight into the solid-state chemistry of pure technetium-99 (Tc) oxides is required in the development of a robust immobilization and disposal system for nuclear waste stemming from the radiopharmaceutical industry, from the production of nuclear weapons, and from spent nuclear fuel. However, because of its radiotoxicity and the subsequent requirement of special facilities and handling procedures for research, only a few studies have been completed, many of which are over 20 years old. In this study, we report the synthesis of pure alkali pertechnetates (sodium, potassium, rubidium, and cesium) and analysis of these compounds by Raman spectroscopy, X-ray absorption spectroscopy (XANES and EXAFS), solid-state nuclear magnetic resonance (static and magic angle spinning), and neutron diffraction.

Conditions for critical effects in the mass action kinetics equations for water radiolysis.

We report on a subtle global feature of the mass action kinetics equations for water radiolysis that results in predictions of a critical behavior in H2O2 and associated radical concentrations. While radiolysis kinetics have been studied extensively in the past, it is only in recent years that high-speed computing has allowed the rapid exploration of the solution over widely varying dose and compositional conditions. We explore the radiolytic production of H2O2 under various externally fixed conditions of molecular H2 and O2 that have been regarded as problematic in the literature-specifically, "jumps" in predicted concentrations, and inconsistencies between predictions and experiments have been reported for α radiolysis.

A non-aqueous reduction process for purifying ¹⁵³Gd produced in natural europium targets.

Gadolinium-153 is a low-energy gamma-emitter used in nuclear medicine imaging quality assurance. Produced in nuclear reactors using natural Eu₂O₃ targets, ¹⁵³Gd is radiochemically separated from europium isotopes by europium reduction. However, conventional aqueous europium reduction produces hydrogen gas, a flammability hazard in radiological hot cells.

Production of high-purity radium-223 from legacy actinium-beryllium neutron sources.

Radium-223 is a short-lived alpha-particle-emitting radionuclide with potential applications in cancer treatment. Research to develop new radiopharmaceuticals employing (223)Ra has been hindered by poor availability due to the small quantities of parent actinium-227 available world-wide. The purpose of this study was to develop innovative and cost-effective methods to obtain high-purity (223)Ra from (227)Ac.

Probing the oxygen environment in UO(2)(2+) by solid-state 17O nuclear magnetic resonance spectroscopy and relativistic density functional calculations.

A combined theoretical and solid-state (17)O nuclear magnetic resonance (NMR) study of the electronic structure of the uranyl ion UO(2)(2+) in (NH(4))(4)UO(2)(CO(3))(3) and rutherfordine (UO(2)CO(3)) is presented, the former representing a system with a hydrogen-bonding environment around the uranyl oxygens and the latter exemplifying a uranyl environment without hydrogens. Relativistic density functional calculations reveal unique features of the U-O covalent bond, including the finding of (17)O chemical shift anisotropies that are among the largest for oxygen ever reported (>1200 ppm). Computational results for the oxygen electric field gradient tensor are found to be consistently larger in magnitude than experimental solid-state (17)O NMR measurements in a 7.