Hydrogen production during the irradiation of gaseous organic compounds: advantage of an extracted beam

ACE, Accélérateur, NIMBInternational audienceThis paper presents a fundamental study of the radiolysis of gaseous organic molecules induced by proton beam. For that purpose, a specific extracted beam line associated with a gas irradiation cell was set up on the 4 MV facility of the Institut de Physique Nucléaire of Lyon. The first experiments have been performed with gaseous alkanes and alkenes. The gaseous species formed during irradiation are analysed by an on-line gas chromatography instrument equipped with two detectors. In order to test our experimental faiclity, we have studied the influence of irradiation parameters (duration, beam intensity, pressure) on the production of hydrogen. In the case of propane, the radiolytic yield value of hydrogen G(H$_2$) is equal to 3.7 for total does in the range of 0.4 to 2.3 MGy at atmospheric pressure

Modifications of oxidized Zircaloy-4 surface in contact with radiolysed wet air

International audienceIn the framework of radioactive waste geological disposal, the long term evolution of the nuclear wastes packages and the release of the radionuclides from the wastes have to be studied. Regarding compacted wastes (cladding tubes) coming from reprocessing of spent fuel, the Zircaloy-4 (zirconium alloy) cladding tubes have been activated and oxidized in reactors. In the disposal, the radioactive waste is exposed to humid air in a first phase and to water after the resaturation phase. In order to better assess the degradation process of these nuclear waste package, the influence of wet air proton radiolysis on the behavior of surface oxidized Zircaloy-4 has been investigated. Radiolysis experiments were performed using an irradiation cell which is associated to an extracted beam. Samples are exposed to wet air, under and without radiolysis, during 12 and 24 h. The water partial pressure has been fixed at 6 and 50 mbar in order to have, respectively, localized adsorbed water molecules and a thin film of adsorbed water. Before and after each treatment, sample surfaces were characterized by X-ray Photoelectron Spectroscopy (XPS) in order to identify the elements at the topmost surface of the solid. The wet air radiolysis causes changes at the surface of oxidized Zircaloy-4 and influences the corrosion phenomenon. Indeed, an enrichment of tin and the presence of nitrogen species were observed. It could be due to the formation of tritin(II) tetrahydroxide dinitrate and a Zr4+ tetramer on the topmost oxide surface

Hierarchically Porous Gd3+-Doped CeO2 Nanostructures for the Remarkable Enhancement of Optical and Magnetic Properties

Rare earth ion-doped CeO2 has attracted more and more attention because of its special electrical, optical, magnetic, or catalytic properties. In this paper, a facile electrochemical deposition route was reported for the direct growth of the porous Gd-doped CeO2. The formation process of Gd-doped CeO2 composites was investigated. The obtained deposits were characterized by SEM, EDS, XRD, and XPS. The porous Gd3+- doped CeO2 (10 at% Gd) displays a typical type I adsorption isotherm and yields a large specific surface area of 135 m2/g. As Gd3+ ions were doped into CeO2 lattice, the absorption spectrum of Gd3+-doped CeO2 nanocrystals exhibited a red shift compared with porous CeO2 nanocrystals and bulk CeO2, and the luminescence of Gd3+-doped CeO2 deposits was remarkably enhanced due to the presence of more oxygen vacancies. In addition, the strong magnetic properties of Gd-doped CeO2 (10 at% Gd) were observed, which may be caused by Gd3+ ions or more oxygen defects in deposits. In addition, the catalytic activity of porous Gd-doped CeO2 toward CO oxidation was studied

LOW PRESSURE CHEMICAL VAPOR DEPOSITION OF TIN OXIDE THIN FILMS FROM AN ORGANOMETALLIC COMPOUND. APPLICATION TO GAS DETECTION

Tin dioxide SnO2 is one of the most common materials used in the fabrication of semiconductor gas sensors The principle of such sensors is based upon the variations of conductivity induced by adsorption of various gases. A low pressure OMCVD apparatus has been developed in order to obtain tin dioxide thin films. Structural and electrical properties have been investigated by different techniques : S.E.M., X-ray diffraction and conductivity measurements in different atmospheres. A correlation is found between the deposition parameters and the electrical properties of CVD-SnO2 thin films

Emploi de la réaction résonnante 1H(15N, αγ) pour l'obtention de profils de concentration d'hydrogène dans les matériaux

Experimental results of hydrogen depth profiling in materials, using the resonant nuclear reaction 1H(15N, αγ) ( ER = 6 385 keV) are presented here. Such an analysis can be performed with a 2 500 kV accelerator. Among the problems inherent to such an ion beam analysis, we discuss the influence of the vacuum quality, of the surface state of the targets and of the in-depth hydrogen stability. Nevertheless it turns out that the analytical performances of the method (depth resolution of 50 Å, analysing depth about one micron and sensitivity down to 50 ppm in silicon) make it potentially the most attractive of the nuclear methods. Various examples are given about the problems encountered and the performances reported.Nous présentons ici un ensemble de résultats expérimentaux concernant l'utilisation de la réaction résonnante 1H(15N, αγ) ( ER = 6 385 keV) dans la détermination de profils de concentration d'hydrogène dans différents matériaux. Cette méthode peut être mise en œuvre sur un accélérateur d'au moins 2 500 kV. Parmi les problèmes inhérents à la méthode, l'influence de la qualité du vide, l'état de surface des cibles et la stabilité de l'hydrogène en profondeur sont discutés. Il apparaît cependant que l'ensemble des performances de la méthode (résolution en profondeur de 50 Å, épaisseur analysable de l'ordre du micron et sensibilité voisine de 50 ppm dans le silicium) la place potentiellement au premier rang des méthodes nucléaires actuelles. Divers exemples illustrent les problèmes posés et les performances indiquées

Quantitative gas detection with semiconductor micro-sensors and chemometrics

International audienceThe use of the chemometric techniques to exploit the selectivity of gas sensors, although current in the case of multisensors systems, is tested here with only one gas sensor. The method consists in measuring the electric conductance of the sensitive element, a tin dioxide bar, at various temperatures. Although these gas sensors follow non linear laws, the modelization algorithm Partial Least Square (PLS) is preffered to neurak networks. A comparison of the two algorithms is made, as well as a study of the prediction. Lastly, theconcept is tested on an autonomous prototype in real conditions