A5056949176- Nuclear Materials and Properties
- Radioactive element chemistry and processing
- Catalytic Processes in Materials Science
- Anodic Oxide Films and Nanostructures
- Semiconductor materials and devices
- Nuclear reactor physics and engineering
- Nuclear materials and radiation effects
- Concrete Corrosion and Durability
- Electrochemical Analysis and Applications
- Solar Thermal and Photovoltaic Systems
- Fusion materials and technologies
- Plasma Applications and Diagnostics
- Smart Materials for Construction
- Nuclear Physics and Applications
- Muon and positron interactions and applications
- Corrosion Behavior and Inhibition
- GaN-based semiconductor devices and materials
- Metal and Thin Film Mechanics
- Water Quality Monitoring and Analysis
- Electron and X-Ray Spectroscopy Techniques
- ZnO doping and properties
- Thermal Radiation and Cooling Technologies
- Electronic and Structural Properties of Oxides
- Gas Sensing Nanomaterials and Sensors
- Plasma Diagnostics and Applications
University of Helsinki
2020-2025
Helsinki Institute of Physics
2020-2024
Aalto University
2016-2020
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2012-2016
CEA Cadarache
2014-2016
Direction des énergies
2015-2016
Synchrotron soleil
2014-2016
Centre National de la Recherche Scientifique
1983-2014
Lincoln Land Community College
2014
Université Claude Bernard Lyon 1
2009-2013
A fundamental question concerning the chemical state of uranium in binary oxides UO2, U4O9, U3O7, U3O8, and UO3 is addressed. By utilizing high energy resolution fluorescence detection X-ray absorption near edge spectroscopy (HERFD-XANES) at M4 edge, a novel technique tender region, we obtain distribution formal oxidation states mixed-valence U3O8. Moreover, clearly identify pivot from U(IV)–U(V) to U(V)–U(VI) charge compensation, corresponding with transition fluorite-type structure (U3O7)...
The development of active catalysts for carbon dioxide (CO 2 ) hydrogenation to methanol is intimately related the creation effective metal-oxide interfaces.In this work, we investigated how order addition copper and zinc on zirconia influences catalytic properties, activity selectivity toward methanol.Regarding conversion production, which promoter (zinc) was atomically deposited after impregnation (i.e., ZnO/Cu/ZrO ZnO/Cu/ZnO/ZrO were superior compared reverse copper-after-zinc catalyst...
Abstract The MARS beamline at the SOLEIL synchrotron is dedicated to characterization of radioactive material samples. One great advantage possibility characterize about 380 radionuclides by different X-ray techniques in same place. This facility unique Europe. A wide energy range from around 3.5 keV 36 K-edges K Cs, and L3 edges Cd Am beyond can be used. optimized for absorption spectroscopy (XANES/EXAFS), powder diffraction (XRD) but x-ray fluorescence (XRF) analysis, High Energy...
We report and discuss here the unambiguous uranium valence state determination on complex compound [Ni(H2O)4]3[U(OH,H2O)(UO2)8O12(OH)3] by using high-energy-resolution fluorescence detection-X-ray absorption near-edge structure spectroscopy (HERFD-XANES). The spectra at both U L3- M4-edges confirm that all five nonequivalent atoms are solely in hexavalent form this compound, as previously suggested bond-valence-sum analysis X-ray diffraction pattern refinement. Moreover, presence of preedge...
A comprehensive analysis of X-ray absorption data obtained at the U L3-edge for a systematic series single-valence (UO2, KUO3, UO3) and mixed-valence uranium compounds (U4O9, U3O7, U3O8) is reported. High-energy resolution fluorescence detection (HERFD) near-edge spectroscopy (XANES) extended fine structure (EXAFS) methods were applied to evaluate U(IV) U(V) environments, in particular, investigate U3O7 local structure. We find that valence state distribution cannot be confidently quantified...
<title>Abstract</title> AlGaN alloys with high Al content offer the possibility to create deep ultraviolet (UV) light sources emitting at wavelengths ≤ 240 nm enhanced quantum efficiency. However, pushing limits of band gap energies towards higher values leads problems n-type doping standard choice Si donors when surpasses ∼80 %. This is due formation so-called negative DX center where Si-N bond ruptured, followed by a displacement N atom. In this paper, we show that amphoteric nature dopant...
First-principles calculations have been carried out to study the incorporation of rare gas atoms, with a focus on xenon, in titanium nitride. The density functional theory--generalized gradient approximation method has used calculate formation energy several point defects (vacancies, interstitials, divacancies, Frenkel pairs) and then energies gases these defects. main results show that nitrogen vacancies are most probable as well Schottky Incorporation suggest favorable Xe host sites...
We report here the direct experimental observation of preferential xenon incorporation site in uranium dioxide and analyse how its evolves with annealing temperature. show that High Energy Resolution Fluorescence Detection X-ray Absorption Near Edge Structure combination first-principles calculations enable a precise determination Xe site. Our finding provides important insight for understanding modeling noble gases behavior nuclear oxide fuel.
The evolution of the uranium chemical state in compounds, principally oxides, is concern context nuclear fuel degradation under storage and repository conditions, accident scenarios. U–O system shows complicated phase relations between single-valence dioxide (UO 2 ) different mixed-valence compounds ( e.g. U 4 O 9 , 3 7 8 ). To try resolving electronic structure associated with unique atomic positions, a combined application diffraction spectroscopic techniques, such as anomalous fine...
Abstract Mass Transfer of ozone absorbed by water in a semi-comtinuous stirred reactor is studied at the lab scale. Experimental investigation using complete factorial scheme shows predominant effect agitation speed and gas flow results correlation for mass transfer coefficient, k1a. Solubility estimated evaluation an apparent Henry's law constant different temperatures (20* 50*C), pH values (2 7) t ionic strength (0.13).
Dense TiN and TiC samples were prepared by hot pressing using micrometric powders. Xenon species (simulating rare gas fission products) then implanted into the ceramics. The annealed for 1 h at 1500 °C under several degraded vacuums with PO2 varying from 10−6 to 2×10−4 mbars. oxidation resistance of their retention properties respect preimplanted xenon analyzed scanning electron microscopy, grazing incidence x-ray diffraction, Rutherford backscattering spectrometry, nuclear spectrometry....
Bentonite is one of the materials used to construct engineered barriers in high-level radioactive nuclear waste geological disposal with its many advantageous features such as low hydraulic conductivity, self-sealing ability, durability, adsorption and immobilization metals radionuclides reduction microbial activity. Many these properties are linked bentonite swelling capability. Transformations indigenous microorganism communities from Wyoming-type Finnish repository site groundwater their...
Uranium-americium mixed oxides could be used as transmutation targets to lower Am inventory in spent nuclear fuels. Due (241)Am activity, these materials are subjected α-self-irradiation which provokes crystallographic disorder. Previous studies on U-Am gave first insight into α-radiation tolerance of compounds, but have never been carried out for more than a year, whereas compounds might stored up few years between fabrication and irradiation. In this work, we study effects self-irradiation...
The valence band electronic structures of mixed uranium oxides (UO2, U4O9, U3O7, U3O8, and β-UO3) have been studied using the resonant inelastic X-ray scattering (RIXS) technique at U M5 edge computational methods. We show here that RIXS recorded 5f-O 2p charge transfer excitations can be used to test validity theoretical approximations.
Herein, the results of positron lifetime and X‐ray absorption spectroscopy obtained in Si‐doped GaN crystals, grown by hydride vapor phase epitaxy (HVPE), are reported. Pushing Si doping to high concentrations leads surprisingly strong compensation effects. Positron experiments show that Ga vacancies not enough be efficient centers. Other acceptor‐like impurities present orders magnitude lower than content samples. shows local environment dopants compensated samples is different from fully...