Insight into the Cationic Charge Distribution in UPuAmO Mixed Oxides.

Uranium-plutonium mixed oxides, containing few mol % of Am, are currently studied as fuel for Sodium Fast Reactors. The study of the O/M ratio of these fuels is of main interest, as its variation can induce issues for reactor safety. For this purpose, four UPuAmO samples (0.

Determination of Uranium Central-Field Covalency with 34 Resonant Inelastic X-ray Scattering.

Understanding the nature of metal-ligand bonding is a major challenge in actinide chemistry. We present a new experimental strategy for addressing this challenge using actinide 34 resonant inelastic X-ray scattering (RIXS). Through a systematic study of uranium(IV) halide complexes, [UX], where X = F, Cl, or Br, we identify RIXS spectral satellites with relative energies and intensities that relate to the extent of uranium-ligand bond covalency.

Pentavalent U Reactivity Impacts U Isotopic Fractionation during Reduction by Magnetite.

Meaningful interpretation of U isotope measurements relies on unraveling the impact of reduction mechanisms on the isotopic fractionation. Here, the isotope fractionation of hexavalent U [U(VI)] was investigated during its reductive mineralization by magnetite to intermediate pentavalent U [U(V)] and ultimately tetravalent U [U(IV)]. As the reaction proceeded, the remaining aqueous phase U [containing U(VI) and U(V)] systematically carried light isotopes, whereas in the bicarbonate-extracted solution [containing U(VI) and U(V)], the δU values varied, especially when / approached 0.

Incorporation of U(IV) in monazite-cheralite ceramics under oxidizing and inert atmospheres.

This work is the first attempt to prepare NdCaUPO monazite-cheralite with 0 < ≤ 0.1 by a wet chemistry method. This method relies on the precipitation under hydrothermal conditions ( = 110 °C for four days) of the NdCaUPO·HO rhabdophane precursor, followed by its thermal conversion for 6 h at 1100 °C in air or Ar atmosphere.

Influence of Sintering Conditions on the Structure and Redox Speciation of Homogeneous (U,Ce)O Ceramics: A Synchrotron Study.

Although uranium-cerium dioxides are frequently used as a surrogate material for (U,Pu)O nuclear fuels, there is currently no reliable data regarding the oxygen stoichiometry and redox speciation of the cations in such samples. In order to fill this gap, this manuscript details a synchrotron study of highly homogeneous (U,Ce)O sintered samples prepared by a wet-chemistry route. HERFD-XANES spectroscopy led to determining accurately the O/M ratios (with M = U + Ce).

To form or not to form: PuO nanoparticles at acidic pH.

The aim of this study is to synthesize PuO nanoparticles (NPs) at low pH values and characterize the materials using laboratory and synchrotron-based methods. Properties of the PuO NPs formed under acidic conditions (pH 1-4) are explored here at the atomic scale. High-resolution transmission electron microscopy (HRTEM) is applied to characterize the crystallinity, morphology and size of the particles.

Uranium retention on iron oxyhydroxides in post-mining environmental conditions.

Investigating uranium migration mechanisms related to the weathering of waste rocks is essential for developing strategies that can address the potential environmental issues caused by uranium mining. This work is based on environmental samples containing 2 L ferrihydrite, lepidocrocite and goethite collected in the technosols from granitic waste rock piles, mine drainage conduits and mine waters. The results show the important role of iron oxyhydroxide in U immobilization and re-concentration.

Hydrothermal Conversion of Thorium Oxalate into ThO·HO Oxide.

Hydrothermal conversion of thorium oxalate, Th(CO)·HO, into thorium dioxide was explored through a multiparametric study, leading to some guidelines for the preparation of crystallized samples with the minimum amount of impurities. As the formation of the oxide appeared to be operated through the hydrolysis of Th after decomposition of oxalate fractions, pH values typically above 1 must be considered to recover a solid phase. Also, because of the high stability of the thorium oxalate precursor, hydrothermal treatments of more than 5 h at a temperature above 220 °C were required.

Synthesis, Structural, and Electronic Properties of KPuO(CO): An Environmentally Relevant Plutonium Carbonate Complex.

The chemical properties of actinide materials are often predefined and described based on the data available for isostructural species. This is the case for potassium plutonyl () carbonate, KPuO(CO), a complex relevant for nuclear technology and the environment, of which the crystallographic and thermodynamic properties of which are still lacking. We report here the synthesis and characterization of achieved by single-crystal X-ray diffraction analysis and high-energy-resolution fluorescence-detected X-ray absorption near-edge structure at the Pu M-edge coupled with electronic structure calculations.

The missing pieces of the PuO nanoparticle puzzle.

The nanoscience field often produces results more mystifying than any other discipline. It has been argued that changes in the plutonium dioxide (PuO) particle size from bulk to nano can have a drastic effect on PuO properties. Here we report a full characterization of PuO nanoparticles (NPs) at the atomic level and probe their local and electronic structures by a variety of methods available at the synchrotron, including extended X-ray absorption fine structure (EXAFS) at the Pu L edge, X-ray absorption near edge structure (XANES) in high energy resolution fluorescence detection (HERFD) mode at the Pu L and M edges, high energy X-ray scattering (HEXS) and X-ray diffraction (XRD).

Oxidation as an Early Stage in the Multistep Thermal Decomposition of Uranium(IV) Oxalate into UO.

The thermal decomposition of actinide oxalates is greatly dependent on the oxidation state of the cation, the gas involved, and the physical characteristics of the precursor. In the actinides series, uranium(IV) oxalate U(CO)·6HO can be viewed as a peculiar case, as its sensibility toward oxidation leads to a specific series of reactions when heating under an oxygen atmosphere. In order to clarify the disagreements existing in the literature, particularly concerning potential carbonate intermediates and the possible transitory existence of UO, we show here an extended characterization of the different intermediates through a combination of X-ray diffraction, vibrational spectroscopies and X-ray absorption near-edge spectroscopy.

Oxygen K-edge X-ray Absorption Spectra.

We review oxygen K-edge X-ray absorption spectra of both molecules and solids. We start with an overview of the main experimental aspects of oxygen K-edge X-ray absorption measurements including X-ray sources, monochromators, and detection schemes. Many recent oxygen K-edge studies combine X-ray absorption with time and spatially resolved measurements and/or operando conditions.

Hydrothermal Conversion of Uranium(IV) Oxalate into Oxides: A Comprehensive Study.

Within the development of future nuclear reactors, wet chemistry routes have been investigated for the fabrication of advanced oxide fuels. In this frame, a multiparametric study focused on the hydrothermal conversion of uranium(IV) oxalate U(CO)·HO into uranium oxides was undertaken in order to unravel the effects of temperature, pH, and kinetics. For pH ≤ 1, the lowest temperatures explored (typically from 180 to 200 °C) led to stabilized UO/UO mixtures exhibiting a global O/U ratio evaluated as 2.

Speciation Change of Uranyl in Lithium Borate Glasses.

Determining the uranyl(VI) UO reactivity in crystalline and amorphous oxides is necessary to control its mobility. The intrinsic versatility of borate structural units containing both triangular BO and tetrahedral BO makes them original and rich hosts for uranyl. As part of the effort to determine the uranium stability in borate oxides, we have determined the speciation of uranium(VI) in two lithium borate glasses containing, respectively, 10 mol % and 30 mol % LiO using a combined structural and spectroscopic approach based on X-ray absorption spectroscopy (XAS).

The Grande Rose of the Reims Cathedral: an eight-century perspective on the colour management of medieval stained glass.

The Grande Rose of Reims Cathedral (France), a UNESCO Cultural Heritage Monument from the 13 century, underwent several restoration works during the 20 century. Its colours result from centuries of colour management from which little information remain. We used non-destructive and portable optical absorption spectroscopy to quantify glass colour and determine the colouring species on a large-scale study of this monumental window.

Direct Observation of Cr 3d States in Ruby: Toward Experimental Mechanistic Evidence of Metal Chemistry.

The role of transition metals in chemical reactions is often derived from probing the metal 3d states. However, the relation between metal site geometry and 3d electronic states, arising from multielectronic effects, makes the spectral data interpretation and modeling of these optical excited states a challenge. Here we show, using the well-known case of red ruby, that unique insights into the density of transition metal 3d excited states can be gained with 2p3d resonant inelastic X-ray scattering (RIXS).

Local vs Nonlocal States in FeTiO Probed with 1s2pRIXS: Implications for Photochemistry.

Metal-metal charge transfer (MMCT) is expected to be the main mechanism that enables the harvesting of solar light by iron-titanium oxides for photocatalysis. We have studied FeTiO as a model compound for MMCT with 1s2pRIXS at the Fe K-edge. The high-energy resolution XANES enables distinguishing five pre-edge features.

Nondestructive Redox Quantification Reveals Glassmaking of Rare French Gothic Stained Glasses.

The sophisticated colors of medieval glasses arise from their transition metal (TM) impurities and capture information about ancient glassmaking techniques. Beyond the glass chemical composition, the TM redox is also a key factor in the glass color, but its quantification without any sampling is a challenge. We report a combination of nondestructive and noninvasive quantitative analyses of the chemical composition by particle-induced X-ray emission-particle-induced γ-ray emission mappings and of the color and TM element speciation by optical absorption spectroscopy performed on a red-blue-purple striped glass from the stained glass windows of the Sainte-Chapelle in Paris, France, during its restoration.

Assessment of Transition Element Speciation in Glasses Using a Portable Transmission Ultraviolet-Visible-Near-Infrared (UV-Vis-NIR) Spectrometer.

A new low-cost experimental setup based on two compact dispersive optical spectrometers has been developed to measure optical absorption transmission spectra over the 350-2500 nm energy range. We demonstrate how near-infrared (NIR) data are essential to identify the coloring species in addition to ultraviolet visible data. After calibration with reference glasses, the use of an original sample stage that maintains the window panel in the vertical position enables the comparison of ancient and modern glasses embedded in a panel from the Sainte-Chapelle of Paris, without any sampling.

Generation of time-bin entangled photon pairs by cascaded second-order nonlinearity in a single periodically poled LiNbO(3) waveguide.

Entangled photon pairs are one of the most important resources for the development of quantum communication technologies. In order to produce pulsed photon pairs in the telecommunication band from 1.5 mum pump light, most of the previous experiments used two successive periodically poled lithium niobate (PPLN) waveguides.