T. Gouder
Institute for Transuranium Elements
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Publication
Featured researches published by T. Gouder.
Journal of Alloys and Compounds | 2001
Leon Black; F. Miserque; T. Gouder; Ladislav Havela; J. Rebizant; Franck Wastin
Abstract Thin films of UN and U 2 N 3 were prepared by reactive DC sputtering of U in N 2 -containing atmosphere. The composition of the films was modified by varying the partial pressure of N 2 . 4f-Core-level photoelectron spectra as well as valence-band spectra obtained with HeII and HeI photoexcitation confirm the itinerant character of the 5f-electronic states in UN, showing a high density of states at the Fermi energy. The 4f peaks in U 2 N 3 are shifted towards higher binding energy and are symmetric, indicating a low density of states at the Fermi level. Valence-band spectra show indeed a maximum of 5f emission at 0.8 eV below the Fermi level, but some 5f intensity at the Fermi level is preserved, contradicting full 5f localisation.
Journal of Nuclear Materials | 2001
S. Van den Berghe; F. Miserque; T. Gouder; B. Gaudreau; M. Verwerft
The use of sputter deposited thin layers of UO 2 as a model system for the investigation of fuel-fission product interactions is presented. The representativity of the layers for the bulk system will be validated and it will be shown, both on theoretical and experimental grounds, that layers of stoichiometric UO 2 can be produced by this method. A comparison will be made between X-ray photoelectron spectroscopic (XPS) results on bulk UO 2 and on the deposited layers. The films deposited can easily be doped with other elements, such as fission products, by codepositing these elements with the UO 2 . This codeposition technique has subsequently been used to produce layers of UO 2 containing cesium. It will be demonstrated that the codeposition with cesium produces uranium in higher valence states (up to U VI ), while without cesium, no higher uranium valencies can be obtained.
Physical Review B | 2006
Alexander B. Shick; L. Havela; Jindrich Kolorenc; Václav Drchal; T. Gouder; Peter M. Oppeneer
The around-mean-field LSDA+U correlated band theory is applied to investigate the electronic and magnetic structure of fcc-Pu-Am alloys. Despite a lattice expansion caused by the Am atoms, neither ...
Chemistry: A European Journal | 2012
Damien Hudry; Christos Apostolidis; Olaf Walter; T. Gouder; Eglantine Courtois; Christian Kübel; Daniel Meyer
The huge interest of the scientific community in the controlled synthesis, structural characterization and assembly into 2and 3-dimensional architectures of nano-objects as well as investigations of their corresponding chemical and physical properties cannot be denied anymore. Within the past two decades, it has been shown that size reduction means more than simply making things smaller. Indeed, size decreasing (as well as shape controlling) is a powerful way to tune materials properties (magnetic, electronic, optical, catalytic, etc.). Whereas nanoscience is a very active field when one considers stable elements, it is still in its infancy when dealing with radioactive actinides. Actinide compounds are important in the nuclear industry and actinide-based nano-objects could be used as new building blocks for the preparation of innovative nuclear fuels or as model systems to study the migration of radionuclides in the environment (e.g., in nuclear waste disposal). The actinide series is also characterized by the emergence of 5f electrons in the valence shell. The behaviour of the 5f electrons determines the solid-sate properties of the actinides and their compounds. Compared to the stable elements, questions related to size and shape effects on the physical and chemical properties of actinide compounds are still open and should find their way into the nanoscience. Accordingly, our main goal is dedicated to the controlled synthesis, the structural characterization and the investigation of the properties of actinide-based nano-objects. Here, we report on the controlled synthesis of uranium oxide and thorium oxide nanocrystals (NCs) by a non-aqueous approach. The obtained NCs have been characterized by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results of this study therefore present an important step for moving to the preparation of transuranium oxide NCs (e.g., NpO2, PuO2). Uranium and thorium oxide NCs were synthesized by the so-called “heating-up” method by using standard air-free techniques. Uranyl acetylacetonate (UO2ACHTUNGTRENNUNG(acac)2) or thorium acetylacetonate (ThACHTUNGTRENNUNG(acac)4) are introduced in a degassed mixture of dibenzyl ether (BnOBn) with different concentrations of stabilizing agents, like oleic acid (OA), oleylACHTUNGTRENNUNGamine (OAm), trioctylamine (N ACHTUNGTRENNUNG(Oct)3) and trioctylphosphine oxide (OP ACHTUNGTRENNUNG(Oct)3). The resulting mixtures are then heated up to 280 8C. After being cooled to room temperature, the NCs are precipitated with ethanol followed by centrifugation and re-dispersion in toluene. Surprisingly, the experimental conditions well-suited for the formation of uranium oxide NCs cannot be applied when considering the formation of thorium oxide NCs. The modification of the reactivity (for a given organic system) as a function of the nature of the actinide precursor and/or the actinide centre seems to be essential when taking into account the synthesis of actinide oxide NCs. Because of these differences in the reactivity of uranium and thorium precursors, different solvent compositions were tested in order to find the best reaction conditions to obtain well defined NCs. A black precipitate can be isolated from the reaction of UO2ACHTUNGTRENNUNG(acac)2 in a mixture of BnOBn/OA/OAm. The PXRD data of the as-prepared compound along with the corresponding Rietveld refinement are presented in Figure 1 a. The PXRD pattern exhibits Bragg reflections characteristic of the fluorite structure (space group Fm-3m). The experimental PXRD pattern was calculated by using the bulk structure of uranium dioxide (UO2). The detailed results of the Rietveld refinement are given in the Supporting Information. The peak broadening is the result of the small size of the coherent domains (the crystallites), which has been estimated with the fundamental approach to be 4.5 nm. Under the same experimental conditions (i.e., BnOBn/ OA/OAm), the reaction of ThACHTUNGTRENNUNG(acac)4 did not give rise to the formation of thorium-based NCs. Indeed, in the presence of [a] Dr. D. Hudry, Dr. C. Apostolidis, Dr. O. Walter, Dr. T. Gouder European Commission: Joint Research Center Institute for Transuranium Elements, P. O. Box 2340 76125 Karlsruhe (Germany) Fax: (+49) 7247-951-599 E-mail : [email protected] [email protected] [b] Dr. E. Courtois, Dr. C. K bel Karlsruhe Institute of Technology, Institute of Nanotechnology Hermann-von-Helmholtz-Platz 1 76344 Eggenstein–Leopoldshafen (Germany) [c] Dr. C. K bel Karlsruhe Nano Micro Facility, Hermann-von-Helmholtz-Platz 1 76344 Eggenstein–Leopoldshafen (Germany) [d] Dr. D. Meyer Institut de Chimie S parative de Marcoule, UMR 5257 BP 17171, 30207 Bagnols sur C ze Cedex (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201200513.
Chemistry: A European Journal | 2013
Damien Hudry; Christos Apostolidis; Olaf Walter; T. Gouder; Eglantine Courtois; Christian Kübel; Daniel Meyer
Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well-defined actinide-based nanocrystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non-aqueous surfactant-assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra-small diameters of 1 nm) of thorium oxide were synthesised.
Journal of Nuclear Materials | 2001
Frédéric Miserque; T. Gouder; D.H. Wegen; Paul David William Bottomley
Abstract UO 2 films have been prepared by dc reactive sputtering of a uranium metal target in an Ar/O 2 atmosphere. We have used the films deposited on gold substrates as working electrodes for electrochemical investigations as simulating the surfaces of fuel pellets. Film composition was determined by photoelectron spectroscopy (XPS and UPS) and X-ray diffraction (XRD). The oxide stoichiometry as a function of deposition conditions was determined and the appropriate conditions for UO 2.0 formation established. AC impedance and cyclic voltammetry measurements were performed. A double RC electrical equivalent circuit was used to fit the data from impedance measurements, similar to those used in unirradiated UO 2 or spent fuel pellets. However due to the porosity or adhesion defects on the thin films that permitted a direct contact between the solution and the gold substrate, we were obliged to add a contribution simulating the water–gold system. Cyclic voltammetry measurements show the influence of pH on the dissolution mechanism. Alkaline solutions permit the formation of an oxidised layer (UO 2.33 ) which is not present in the acidic solutions. In both pH=2 and pH=6 solutions, a U VI species layer is formed.
EPL | 2007
Alexander B. Shick; Jindurich Kolorenč; L. Havela; Václav Drchal; T. Gouder
We propose a straightforward and efficient procedure to perform dynamical mean-field (DMFT) calculations on the top of the static mean-field LDA+U approximation. Starting from self-consistent LDA+U ground state we included multiplet transitions using the Hubbard-I approximation, which yields a very good agreement with experimental photoelectron spectra of δ-Pu, Am, and their selected compounds.
Applied Radiation and Isotopes | 2008
Alfred Morgenstern; Christos Apostolidis; Frank Bruchertseifer; R. Capote; T. Gouder; Federica Simonelli; M. Sin; Kamel Abbas
(230)U/(226)Th is a promising novel alpha-emitter system for application in targeted alpha therapy of cancer. The therapeutic nuclides can be produced by proton irradiation of natural (232)Th according to the reaction (232)Th(p,3n)(230)Pa, followed by subsequent beta decay of (230)Pa to (230)U. In this study, the experimental excitation function for the (232)Th(p,3n)(230)Pa reaction up to 34 MeV proton energy has been measured using the stacked-foil technique. The proton energies in the various foils were calculated with the SRIM 2003 code and gamma-ray spectrometry was used to measure the activities of the various radioisotopes produced. The measured cross-sections are in good agreement with selected literature values and with model calculations using the EMPIRE II code. The reaction (232)Th(p,3n)(230)Pa allows the production of carrier-free (230)U in clinically relevant levels.
Surface Science | 1990
T. Gouder; C.A. Colmenares; J.R. Naegele; J. Verbist
Abstract Ultraviolet photoelectron spectroscopy (UPS) has been used to study the early reaction of uranium with O 2 in the temperature range from 73 to 573 K. Oxygen was shown to be present on the surface in three different states depending on temperature and exposure conditions. An initial dissociative O 2 adsorption at 300 and 573 K was followed by the formation of substoichiometric UO 2−x and hyperstoichiometric UO 2+x at 73 K. UPS turned out to be an extremely powerful technique to study this type of surface reactivity problem. Observation of peak shapes, intensities and binding energies allowed us to develop a unified description of the different steps in the surface oxidation.
Journal of Alloys and Compounds | 1998
T. Gouder
Abstract Surface science research at the ITU is focused on the synthesis and surface spectroscopy studies of thin films of actinides and actinide compounds. The surface spectroscopies used are X-ray and ultra violet photoelectron spectroscopy (XPS and UPS, respectively), and Auger electron spectroscopy (AES). Thin films of actinide elements and compounds are prepared by sputter deposition from elemental targets. Alloy films are deposited from corresponding alloy targets and could be used, in principle, as replicates of these targets. However, there are deviations between alloy film and target composition, which depend on the deposition conditions, such as pressure and target voltage. Mastering of these effects may allow us to study stoichiometric film replicates instead of thick bulk compounds. As an example, we discuss the composition of U–Ni films prepared from a UNi 5 target.