Modification des propriétés de surface de poudres en lit fluidisé assisté par une post-décharge

Cette thèse a concerné l'étude d'un procédé original de traitement de surface de poudres thermosensibles par un gaz à basse température et basse pression. Ce procédé a consisté à coupler deux technologies : un lit fluidisé gaz-solide et une post-décharge d'azote. La fluidisation assure un bon contact gaz-solide et un traitement uniforme, en induisant d'importants transferts de matière entre les deux phases. La fluidisation est assurée par de l'azote ayant préalablement traversé une décharge micro-onde qui confère à l'azote une réactivité importante même à distance de la décharge. Dans cette étude, la hauteur du lit fixe est de l'ordre de grandeur de diamètre de la colonne de fluidisation. Cette étude a comporté deux parties : la première a consisté à greffer de nouvelles fonctions à la surface de particules de polyéthylène haute densité, à partir d'un plasma d'azote avec ou sans oxygène. La seconde a été dédiée au dépôt d'oxyde de silicium à partir de silane sur ces mêmes poudres. La première partie a montré qu'il est possible d'augmenter la mouillabilité de cette poudre de polyéthylène, naturellement hydrophobe, mais que l'efficacité du traitement dépend essentiellement de la composition chimique du gaz plasmagène. En effet, un plasma en post décharge d'azote permet d'augmenter la mouillabilité, mais uniquement par rapport à un liquide organique. Le fait d'ajouter un peu d'oxygène rend plus efficace le traitement en diminuant drastiquement l'angle de contact à l'eau. La deuxième partie a démontré la faisabilité d'un dépôt d'oxyde de silicium à basse température (<90°C), à partir de silane injecté au niveau du lit fluidisé. La continuité du dépôt et la mouillabilité de la poudre traitée augmentent avec les débits d'oxygène et de silane. Des études de vieillissement ont montré que le comportement en mouillabilité des poudres les plus couvertes est très proche de celui de la silice.This work concerns the development of an original process which consists in coupling two technologies: fluidized bed and cold nitrogen remote-plasma. The main object of this work is to treat an important weight of thermo-sensitive powders at low temperature and pressure. Besides, our goal also consists in understanding the phenomenon taking place in our process. The fluidized bed is used for improving the gas-solid contact. The fluidization induces a uniform treatment, important mass and thermal transfers between the two phases. The fluidization is achieved by nitrogen, which flows previously through a microwave discharge. The microwave discharge generates chemically active species. In this study, the fixed bed height is of the order of the bed diameter. This work includes two parts: in the first one, the grafting of new chemical functions on the surface of polyethylene powders due to their exposure to a cold nitrogen remote plasma with and without oxygen is studied. The second concerns the deposition of silicon oxide on the same type of powder from silane (SiH4) and oxygen. In the first part, the wettability of polyethylene powders is increased, knowing that the polyethylene powders is naturally hydrophobic. The treatment efficiency depends essentially on the composition of the plasma gas. In fact, a pure nitrogen post-discharge can increase the wettability character of the powder, but only relative to organic liquids. Nevertheless, adding a small amount of oxygen allows reaching a better water wettability. In the second part, the feasibility of depositing silicon oxide on the surface of a polyethylene powder, using a far nitrogen/oxygen cold remote-plasma and silane in a fluidized bed is showed. The deposition occurs under the form of nodules. The powder water wettability is drastically improved by the deposition process. The hydrophilic character and the continuity of the deposit are exalted by the increase of the oxygen concentration injected in the discharge. Aging studies show that the coated-powder wettablity reaches a value similar to that of silica after a few days

Investigation of the 238U(d, p) surrogate reaction via the simultaneous measurement of γ -decay and fission probabilities

We investigated the 238U(d,p) reaction as a surrogate for the n + 238U reaction. For this purpose we measured for the first time the γ -decay and fission probabilities of 239U∗ simultaneously and compared them to the corresponding neutron-induced data. We present the details of the procedure to infer the decay probabilities, as well as a thorough uncertainty analysis, including parameter correlations. Calculations based on the continuumdiscretized coupled-channels method and the distorted-wave Born approximation (DWBA) were used to correct our data from detected protons originating from elastic and inelastic deuteron breakup. In the region where fission and γ emission compete, the corrected fission probability is in agreement with neutron-induced data, whereas the γ -decay probability is much higher than the neutron-induced data. We have performed calculations of the decay probabilities with the statistical model and of the average angular momentum populated in the 238U(d,p) reaction with the DWBA to interpret these resultsComisión Europea 26949

A compact fission detector for fission-tagging neutron capture experiments with radioactive fissile isotopes

In the measurement of neutron capture cross-sections of fissile isotopes, the fission channel is a source of background which can be removed efficiently using the so-called fission-tagging or fission-veto technique. For this purpose a new compact and fast fission chamber has been developed. The design criteria and technical description of the chamber are given within the context of a measurement of the 233U(n, ) cross-section at the n_TOF facility at CERN, where it was coupled to the n_TOF Total Absorption Calorimeter. For this measurement the fission detector was optimized for time resolution, minimization of material in the neutron beam and for alpha-fission discrimination. The performance of the fission chamber and its application as a fission tagging detector are discussed.French NEEDS/NACRE ProjectEuropean Commission within HORIZON2020 via the EURATOM Project EUFRA

Nuclear structure of Ac-231

The low-energy structure of 231Ac has been investigated by means of gamma ray spectroscopy following the beta-decay of 231Ra. Multipolarities of 28 transitions have been established by measuring conversion electrons with a mini-orange electron spectrometer. The decay scheme of 231Ra --> 231Ac has been constructed for the first time. The Advanced Time Delayed beta-gamma-gamma(t) method has been used to measure the half-lives of five levels. The moderately fast B(E1) transition rates derived suggest that the octupole effects, albeit weak, are still present in this exotic nucleus

A compact fission detector for fission-tagging neutron capture experiments with radioactive fissile isotopes

© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).In the measurement of neutron capture cross-sections of fissile isotopes, the fission channel is a source of background which can be removed efficiently using the so-called fission-tagging or fission-veto technique. For this purpose a new compact and fast fission chamber has been developed. The design criteria and technical description of the chamber are given within the context of a measurement of the 233U(n, γ) cross-section at the n_TOF facility at CERN, where it was coupled to the n_TOF Total Absorption Calorimeter. For this measurement the fission detector was optimized for time resolution, minimization of material in the neutron beam and for alpha-fission discrimination. The performance of the fission chamber and its application as a fission tagging detector are discussed.Peer reviewe

Les soins d'hygiène bucco-dentaire à l'officine

PARIS-BIUP (751062107) / SudocSudocFranceF

Pandémie gripale 2009, représentations, croyances, connaissances, comportements des médecins généralistes face à la vaccination anti-grippale H1N1v (étude menée auprès de 23 médecins généralistes dans le département des Alpes Maritimes au cours de la campagne vaccinale de masse contre le virus grippal A (H1N1)v 2009)

NICE-BU Médecine Odontologie (060882102) / SudocSudocFranceF