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1
Almayrac, Matthieu. "Volatile element behaviour in cometary ice analogues under irradiation". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0320.
Abstract (sommario):
Les comètes sont parmi les corps les plus primitifs et inaltérés de notre système solaire. Leur étude peut fournir un aperçu unique de la composition chimique du système solaire primitif. De plus, en raison de leur nature riche en élément volatils, les comètes ont probablement joué un rôle crucial dans l'apport d'éléments pré-biotiques (H, C, N et O) et de matières organiques à la Terre primitive. Comprendre comment se forment les comètes peut donc fournir une mine d'informations sur l'évolution de la composition des éléments volatils dans le système solaire, depuis le nuage moléculaire pré-solaire jusqu'à la formation des planètes telluriques. Des décennies d'études cométaires, et la récente mission Rosetta de l'ESA sur la comète 67P/Churyumov-Gerasimenko (67P/C-G), ont démontré que les espèces volatiles piégées dans les comètes ont une composition distincte de tout autre réservoir connu du système solaire. L'azote cométaire, en particulier, présente de forts enrichissements en isotope 15N. L'origine de ces enrichissements reste incertaine, reflétant potentiellement la présence de processus permettant de produire de forts fractionnements isotopiques d'un gaz nébulaire initial pauvre en 15N, ou l'héritage d'un réservoir isotopique riche en 15N inconnu. Au cours de cette thèse, j'ai développé une expérience pour former des glaces cométaires (c'est-à-dire des glaces riches en eau formées à des températures et des pressions très basses), avec l'objectif principal d'explorer comment les éléments volatils (l'azote et les gaz nobles) sont incorporés dans les glaces cométaires à partir de la nébuleuse proto-solaire. Différentes températures de formation (de 28K à 80K) et conditions d'irradiation ont été testées afin d'étudier les paramètres reproduisant le plus fidèlement la composition de la comète 67P/C-G. Les analogues de glace cométaires formés expérimentalement autour de 70K ont des abondances relatives d'azote et de gaz nobles plus proches de celles mesurées dans 67P/C-G que les analogues formés à plus basses températures (≤ 60K). De plus, j'ai mis en évidence que les processus d'incorporation de l'azote et des gaz nobles dans la glace et leur libération ultérieure ne produisent pas de variations isotopiques significatives. Cela indique que les signatures isotopiques des comètes ont très probablement été héritées de leur environnement de formation, et ne résultent pas de processus de fractionnements isotopiques pendant la formation/sublimation de la glace. Enfin, j'ai également étudié l'effet que l'irradiation UV peut avoir sur la composition des gaz piégés dans la glace cométaire. L'irradiation pendant et après le dépôt de glace n'a que peu d'effet sur la composition isotopique des espèces volatiles piégées. Cependant, l'irradiation de la surface de la glace a un effet majeur sur le schéma de libération des gaz piégés. Une glace irradiée conserve ses éléments volatils piégés à des températures supérieures à la température de transition de la glace amorphe à cristalline (120-140K), à l'inverse d'une glace non-irradiée. La rétention prolongée des gaz piégés dans les glaces cométaires irradiées peut avoir des implications majeures sur la capacité des comètes à contribuer à l'apport d'éléments volatils aux planètes du système solaire interneComets represent some of the most pristine and unprocessed bodies in our solar system. As such, their analysis can provide a unique insight into the chemical makeup of the early Solar System. Furthermore, due to their volatile-rich nature, comets may have played an important role in delivering volatile elements (e.g., H, C, N, O) and organic materials to early Earth. Understanding how comets form can therefore provide a wealth of information on how the composition of volatile elements evolved in the solar system, from the pre-solar molecular cloud up until the formation of the terrestrial planets. Decades of cometary studies, and the recent ESA Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P/C-G), have demonstrated that volatile species trapped in comets have a composition that is distinct from any other known reservoir in the Solar System. Cometary nitrogen, in particular, shows strong enrichments in the rare 15N isotope. The origin of these enrichments remains unclear, potentially reflecting the isotopic fractionation of an initial 15N-poor nebular gas, or inheritance from an unknown isotopic reservoir. During this PhD, I have developed an experimental setup to form cometary ices (i.e., water-rich ices formed at very low temperatures and pressures), with the overarching objective of exploring how volatile elements (including N and noble gases) were incorporated into cometary ice during water condensation from the protosolar nebula. Different temperatures of formation (from 28K to 80K) and irradiation conditions have been tested in order to investigate the conditions that best reproduce the actual volatile composition of comet 67P/C-G. It was found that condensing cometary ice analogues at temperatures ~70K is best able to reproduce the nitrogen and noble gas abundances measured in 67P/C-G. Moreover, we discovered that the incorporation of nitrogen and noble gases into, and subsequent release from, cometary ices does not produce significant isotope variations, indicating that isotope signatures in comets were most likely inherited from their environment of formation rather than the result of fractionation during ice formation. Finally, I also investigated the effect that UV irradiation can have on the composition of volatiles trapped within cometary ice. Irradiation during and after ice deposition was found to not have a significant effect on the isotopic composition of the trapped volatile species. However, it was discovered that irradiating the surface of the ice had a major effect on the release pattern of trapped volatiles, with the ice being retentive of trapped volatiles even after the amorphous-to-crystalline ice transition (120-140K), temperatures at which point all trapped volatiles are released from non-irradiated ice. The enhanced retention of volatiles in irradiated cometary ice may have major implications on the potential for comets to deliver volatile elements to the inner solar system
2
Muggiolu, Giovanna. "Deciphering the biological effects of ionizing radiations using charged particle microbeam : from molecular mechanisms to perspectives in emerging cancer therapies". Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0599/document.
Abstract (sommario):
Ces dernières années, le paradigme de la radiobiologie selon lequel les effets biologiques des rayonnements ionisants ne concernent strictement que les dommages à l'ADN et les conséquences liées à leur non réparation ou à leur réparation défectueuse, a été remis en question. Ainsi, plusieurs études suggèrent que des mécanismes «non centrés » sur l'ADN ont une importance significative dans les réponses radio-induites. Ces effets doivent donc être identifiés et caractérisés afin d’évaluer leurs contributions respectives dans des phénomènes tels que la radiorésistance, les risques associés au développement de cancers radio-induits, les conséquences des expositions aux faibles doses. Pour ce faire, il est nécessaire : (i) d'analyser la contribution de ces différentes voies de signalisation et réparation induites en fonction de la dose et de la zone d’irradiation; (ii) d’’étudier les réponses radio-induites suite à l’irradiation exclusive de compartiments subcellulaires spécifiques (exclure les dommages spécifiques à l'ADN nucléaire); (iii) d’améliorer la connaissance des mécanismes moléculaires impliqués dans les phénomènes de radiosensibilité/radiorésistance dans la perspective d’optimiser les protocoles de radiothérapie et d’évaluer in vitro de nouvelles thérapies associant par exemple les effets des rayonnements ionisants et de nanoparticules d’oxydes métalliques. Les microfaisceaux de particules chargées offrent des caractéristiques uniques pour répondre à ces questions en permettant (i) des irradiations sélectives et en dose contrôlée de populations cellulaires et donc l’étude in vitro des effets « ciblés » et « non ciblés » à l'échelle cellulaire et subcellulaire, (ii) de caractériser l’homéostasie de cultures cellulaires en réponses à des expositions aux rayonnements ionisants et/ou aux nanoparticules d’oxydes métalliques (micro-analyse chimique multi-élémentaire). Ainsi, au cours de ma thèse, j'ai validé et exploité des méthodes d’évaluation qualitatives et quantitatives (i) in cellulo et en temps réel de la réponse radio-induite de compartiments biologiques spécifiques (ADN, mitochondrie, …) ; (ii) in vitro de la radiosensibilité de lignées sarcomateuses issues de patients; et (iii) in vitro des effets induits par des expositions à des nanoparticules d'oxydes métalliques afin d’évaluer leur potentiel thérapeutique et anti-cancéreuxFew years ago, the paradigm of radiation biology was that the biological effects of ionizing radiations occurred only if cell nuclei were hit, and that cell death/dysfunction was strictly due to unrepaired/misrepaired DNA. Now, next this “DNA-centric” view several results have shown the importance of “non-DNA centered” effects. Both non-targeted effects and DNA-targeted effects induced by ionizing radiations need to be clarified for the evaluation of the associated radiation resistance phenomena and cancer risks. A complete overview on radiation induced effects requires the study of several points: (i) analyzing the contribution of different signaling and repair pathways activated in response to radiation-induced injuries; (ii) elucidating non-targeted effects to explain cellular mechanisms induced in cellular compartments different from DNA; and (iii) improving the knowledge of sensitivity/resistance molecular mechanisms to adapt, improve and optimize the radiation treatment protocols combining ionizing radiations and nanoparticles. Charged particle microbeams provide unique features to answer these challenge questions by (i) studying in vitro both targeted and non-targeted radiation responses at the cellular scale, (ii) performing dose-controlled irradiations on a cellular populations and (iii) quantifying the chemical element distribution in single cells after exposure to ionizing radiations or nanoparticles. By using this tool, I had the opportunity to (i) use an original micro-irradiation setup based on charged particles microbeam (AIFIRA) with which the delivered particles are controlled in time, amount and space to validate in vitro methodological approaches for assessing the radiation sensitivity of different biological compartments (DNA and cytoplasm); (ii) assess the radiation sensitivity of a collection of cancerous cell lines derived from patients in the context of radiation therapy; (iii) study metal oxide nanoparticles effects in cells in order to understand the potential of nanoparticles in emerging cancer therapeutic approaches
3
Lescoat, Marie-Laure. "Etude du comportement des nano-renforts des matériaux ODS (Oxide Dispersion Strengthened) sous irradiation : Approche analytique par des irradiations aux ions". Thesis, Lille 1, 2012. http://www.theses.fr/2012LIL10167/document.
Abstract (sommario):
Les aciers ferritiques/martensitiques renforcés par dispersion d’oxydes (ODS) sont envisagés pour le gainage combustible des réacteurs à neutrons rapides à caloporteur sodium de quatrième génération. Les nano-oxydes étant à l’origine de la très bonne tenue en fluage à haute température de ces matériaux, il est nécessaire de s’assurer de leur stabilité pour les conditions extrêmes d’irradiation (jusqu’à 200 dpa) et de température (400-700°C) envisagées en service. Ainsi, l’objectif de ces travaux est d’étudier le comportement de ces nano-renforts sous irradiation. Une approche analytique par des irradiations aux ions in-situ et ex-situ est appliquée aux matériaux ODS Fe18Cr1W0,4Ti +0,3 Y2O3 et Fe18Cr1W0,4Ti + 0.3 MgO. Les résultats obtenus montrent notamment que les nano-renforts Y-Ti-O sont capables de résister à de très fortes doses d’irradiation (237 dpa, 500°C) et également que la cohérence des interfaces oxyde/matrice pourrait jouer un rôle important sur le comportement des renforts sous irradiation (stabilité et recombinaison des défauts ponctuels)Oxide Dispersion Strengthened (ODS) Ferritic-Martensitic (FM) alloys are expected to play an important role as cladding material in Generation IV sodium fast reactors operating in extreme temperature (400-500°C) and irradiation conditions (up to 200 dpa). Since nano-oxides give ODS steels their high-temperature strength, the stability of these particles is an important issue. The present study evaluate the radiation response of nano-oxides by the use of in-situ and ex-situ ion irradiations performed on both Fe18Cr1W0,4Ti +0,3 Y2O3 and Fe18Cr1W0,4Ti + 0.3 MgO ODS steels. In particular, the results showed that Y-Ti-O nano-oxides are quite stable under very high dose irradiation, namely 237 dpa at 500°C and, that the oxide interfacial structures are likely playing an important role on the behavior under irradiation (oxide stability and point defect recombination)
4
Petitdidier, Sébastien. "Etude de l'influence de stress électriques et d'irradiations neutroniques sur des HEMTs de la filière GaN". Thesis, Normandie, 2017. http://www.theses.fr/2017NORM2001/document.
Abstract (sommario):
Les transistors HEMTs (High Electron Mobility Transistors) de la filière GaN sont destinés à des applications dans les domaines militaire et spatial. C’est pourquoi nous avons étudié l’influence de trois types de stress électriques : à canal ouvert, à canal pincé et NGB (Negative Gate Bias), ainsi que l’influence de neutrons thermalisés avec une fluence pouvant aller jusqu’à 1,7.1012 neutrons.cm-2, sur leurs performances électriques dc.Dans un premier temps, nous avons étudié des HEMTs AlInN/GaN de laboratoire. Pour les trois stress, nous avons observé une dégradation due à la création de pièges accepteurs et donneurs au cours des différents stress et à la présence de pièges préexistants. Nous avons ensuite irradié ces composants par des neutrons thermalisés et avons observé une légère dégradation des performances électriques des transistors non stressés et stressés à canal ouvert ou pincé. En revanche, nous avons mis en lumière une légère amélioration pour les transistors ayant subi un stress NGB. Nous avons également irradié des MOS-HEMTs AlInN/GaN et conclu que ceux-ci étaient plus sensibles vis à vis des irradiations.Dans un deuxième temps, nous avons stressé de manière analogue des HEMTs AlGaN/GaN du commerce. Dans le cas du stress à canal ouvert, nous avons observé une diminution importante du courant de drain tandis que pour les stress à canal pincé et NGB le courant de drain augmente légèrement à cause d’une libération de pièges préexistants sous l’action du champ électrique vertical. Lors des irradiations avec des neutrons thermalisés, ces transistors, stressés ou non, subissent là encore des dégradationsThe GaN based HEMTs (High Electron Mobility Transistors) are excellent candidates for military and spatial applications. That’s why we have analysed the influence of three different types of bias stress: on-state stress, off-state stress and NGB (Negative Gate Bias), and the influence of thermalized neutrons with a fluence up to 1.7x1012 neutrons.cm-2, on their dc electrical performances.First, we have studied laboratory AlInN/GaN HEMTs. For the three conditions of stress, we have observed a degradation due to pre-existing traps and to the creation of acceptor and donor traps during the stress. Then, we have irradiated these components with thermalized neutrons and we have found a small degradation of the electrical performances of unstressed and on-state stressed and off-state stressed transistors. On the other hand, we have highlighted a slight improvement for NGB stressed components. We have also irradiated AlInN/GaN MOS-HEMTs and we have concluded that they are more sensible to irradiation.In a second time we have stressed in the same way commercial AlGaN/GaN HEMTs. For the on-state stress, we have observed an important increase in the drain current. However, the drain current increases for the on-state and NGB stressed components due to a release of electrons from pre-existing traps under vertical electrical field. During the irradiation with thermalized neutrons, the unstressed and stressed transistors are degraded and a small decrease in the drain current is visible
5
OKA, TOHRU, TOSHIO KANEDA, MINORU UEDA e YASUNORI SUMI. "Effects of Irradiation on Grafted Skin : Vascular Changes after Irradiation". Nagoya University School of Medicine, 1985. http://hdl.handle.net/2237/17473.
6
Misner, Scottie, Carol Curtis e Evelyn Whitmer. "Irradiation of Food". College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2008. http://hdl.handle.net/10150/146430.
Abstract (sommario):
2 pp.Revised version of 1999 title by Meer and Misner
Food irradiation is the treatment of food by a certain type of intense energy known as ionizing radiation. This involves exposing bulk or packaged food to carefully controlled amounts of energy. Food does not come in contact with radioactive material. The publication discusses the technology of food irradiation including; the energy source, effect on foods, identifying treated foods, environmental concerns and approved uses in the U.S.
7
Auvray, Marie-Hélène. "Endommagement sous irradiation de l'aluminate de lithium γ-LiALO₂". Paris 11, 1987. http://www.theses.fr/1987PA112381.
Abstract (sommario):
Cette étude est motivée par l'application potentielle de ce matériau comme couverture tritigene dans les réacteurs de fusion. Elle complète ainsi les études déjà effectuées sur la caractérisation et les mécanismes de production des défauts dans d'autres cristaux ioniques. Irradiation par des projectiles varies (électrons, ions he(+), protons, photons x et gamma) et étude par rpe et absorption optique (détection des défauts ponctuels crées) et par microscopie électronique par transmission (analyse des échantillons avant irradiation et observation des défauts étendus produits par irradiation)
8
Parker, Kerry Ann. "Electron reconstruction and performance studies, search for a heavy Higgs boson decaying to four-leptons using the ATLAS detector, irradiations at the Birmingham Irradiation Facility for the HL-LHC". Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/14390/.
9
Jouanny, Emilie. "Étude de l'évolution microstructurale sous irradiation aux ions Ti2+ de deux alliages de titane : lien avec les propriétés mécaniques". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0071/document.
Abstract (sommario):
Ce travail de thèse s’intéresse à l’évolution de la microstructure sous irradiation d’alliages de titane, en vue de leur potentielle utilisation dans le domaine du nucléaire. Une étude paramétrique (température, dose et flux d’irradiation) a donc été menée, à l’aide de simulations d’irradiations neutroniques par des irradiations aux ions (plateforme JANNuS – Saclay), sur les alliages T40 et TA6V, et de caractérisations microstructurales qualitatives et quantitatives post irradiation (MET, analyse d’image, SAT). Ainsi, différents défauts d’irradiation ont été identifiés. En particulier, la présence de boucles à composante dans l’alliage T40 et de précipités riches en vanadium dans l’alliage TA6V a clairement pu être mise en évidence dès la température de 300°C. La microstructure résultante est fortement dépendante des paramètres d’irradiation et de l’alliage de titane considéré. Un effet important de la température (entre 300°C et 430°C) a été noté sur les boucles de dislocations de type pour l’alliage T40 et sur les précipités pour l’alliage TA6V. Les doses et les flux considérés à 300°C ne modifient pas la distribution des défauts des deux alliages. A 430°C, l’augmentation de la dose modifie peu le paysage des boucles de dislocations de type pour l’alliage TA6V contrairement à l’alliage T40. Les précipités, quant à eux ne semblent pas affectés par l’augmentation de la dose. Une analyse des mécanismes mis en jeu est proposée. Enfin, des essais de nano-indentation ont permis une première description du lien microstructure / propriétés mécaniques. A 430°C, l'alliage T40 ne semble pas être impacté mécaniquement par l’évolution de la microstructure avec la dose d’irradiation contrairement à l'alliage TA6VThis PhD work deals with microstructural evolution of titanium alloys under irradiation, due to their potential use in the nuclear field. Parametric study (temperature, dose and irradiation flux) was conducted, using ion irradiations (JANNuS – Saclay platform) to simulate neutron irradiation damage. Two titanium alloys (CP Ti grade 2 and Ti-6Al-4V) were considered and qualitative and quantitative post irradiation microstructural characterizations were done (TEM, image analysis, APT). Thus, various irradiation defects were identified. In particular, presence of -component loops was highlighted in CP Ti grade 2 and vanadium-rich precipitates in Ti-6Al-4V from the temperature of 300°C. Resulting microstructure is hardly depending on irradiation parameters and considered titanium alloys. Important effect of temperature (between 300°C and 430°C) was noted on -type dislocation loops in CP Ti grade 2 and precipitates in Ti-6Al-4V. At 300°C, dose and flux have no effect on the defect distribution of the two titanium alloys. At 430°C, the increase of dose has a little consequence on the -type dislocation loops in Ti-6Al-4V, contrary to the ones observed in CP Ti grade 2. Precipitates, observed in Ti-6Al-4V, do not seem to be affected by the increase of the dose. Analysis of involved mechanisms is proposed. Finally, nano-indentation tests have allowed to get first description of the link between microstructure and mechanical properties. At 430°C, CP Ti grade 2 do not seem to be affected mechanically by the microstructural evolution with the irradiation dose, contrary to Ti-6Al-4V
10
Aitkaliyeva, Assel. "Irradiation Stability of Carbon Nanotubes". [College Station, Tex. : Texas A&M University, 2009. http://hdl.handle.net/1969.1/ETD-TAMU-2009-08-3251.
11
Dubé, Frédéric. "Spiral irradiation in stereotactic radiosurgery". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0016/MQ55049.pdf.
12
Dubé, Frédéric 1973. "Spiral irradiation in stereotactic radiosurgery". Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29884.
Abstract (sommario):
The aim of stereotactic radiosurgery is to deliver a high and uniform radiation dose to the target volume and a minimized dose to the surrounding healthy tissue. Various linac-based radiosurgical techniques are used clinically: multiple non-coplanar converging arcs, dynamic arc rotation, and conical rotation. The techniques differ in their beam distribution over the patient's head.A study of the beam distribution characteristics for the clinical linac-based radiosurgical techniques is presented. Two spiral linac-based radiosurgical techniques are developed: the uniform dose-rate spiral irradiation and the dose-rate-weighted spiral irradiation. Both exhibit the same spiraling beam entry trace over the patient's head; however, they differ in their beam distribution along the spiral. The dose-rate-weighted spiral irradiation provides a uniform beam distribution over the 2pi solid angle available in radiosurgery.
The currently existing techniques and the spiral techniques are then compared using the cumulative dose-volume histogram (CDVH) tools available with the McGill Treatment Planning System (MPS). The dose-rate-weighted spiral technique leads to lower dose inhomogeneities within the target volume and better dose conformity within the target. Moreover, it also encompasses smaller volumes of tissue at all isodose levels with larger differences at low isodose levels. A conclusion is reached that the dose-rate-weighted spiral irradiation technique offers interesting advantages over the currently used clinical linac-based techniques.
13
Shaibani, S. J. "Electron irradiation damage of spinal". Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371580.
14
Gelbart, W. "Bulk liquid-metal irradiation system". Helmholtz-Zentrum Dresden - Rossendorf, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-165893.
Abstract (sommario):
Introduction
Low melting point metals are often encapsulated in a hermetic container, irradiated and the container transferred to hot-cell for material removal and processing. An important process of this kind is the production of 82Sr from rubidium (melting point: 39.5 °C.)
This new concept departures completely form the encapsulated targets approach and allows an almost continues production by the irradiation of the bulk metal. As well, eliminated is the target transfer. By placing the target material dissolution chamber right in the target station, only the dissolution product is pumped to the hotcell for further processing.
Material and Methods
Some of the disadvantages of the encapsulated target are:
1. Complicated transfer system that is ex-pensive to install, slow and prone to failures.
2. Complex and expensive encapsulation procedure.
3. Loss of production time during the lengthy target changing.
4. Capsule geometry is constrained by the encapsulating process and transfer demands compromising heat transfer and beam power.
To avoid the difficulties of liquid metal handling, metal salts are often used instead (rubidium chloride is one example). This creates other problems and limits the beam currents and production yields.
In the system described, the liquid metal is transferred (by gravity) from a bulk container to an irradiation chamber. The chamber, made out of nickel-plated silver, holds the correct quantity of rubidium for one irradiation run. Because of the geometry of the chamber and the efficient cooling, up to 40KW of beam power can be delivered to the target. The chamber is equipped with thermocouples and a liquid-metal level detector and is entirely of welded/brazed construction. The alloy foil that forms the beam window is electron-beam welded to the chamber front ring.
At the end of irradiation the irradiated liquid metal is gravity fed into a reaction chamber situ-ated below the irradiation chamber, and a new load of fresh rubidium released into the irradia-tion chamber. The liquid-metal transfer and the irradiation components are shown on FIG. 1, and the sectional view on FIG. 2.
Appropriate chemicals (n-butanol in the case of rubidium) are delivered to the reaction chamber and the irradiated metal dissolved. The liquid dissolution product is transferred back to the hotcell. Since all steps of the reaction involve liquids, only small diameter tubes connect the target station with the hotcell. The transfer is fast and simple.
The bulk liquid-metal storage container can be constructed to hold enough material for 10 or more runs. When empty, it is replaced with a pre-loaded one. The container is connected to the target system with one coupling and the exchange takes a short time. A robotic bottle exchange can be implemented if desired.
The station is equipped with its own vacuum system, beam diagnostic (consisting of a four-sector mask) and a collimation. The target chamber and each of the beam intercepting components are electrically insulated to allow beam current monitoring.
Constructed entirely out of metal and ceramic the target core assembly does not suffer from radiation damage. The use of aluminum, silver and alumina reduce component activation.
Results and Conclusion
A large part of the station design is based on the well proven construction of high current solid target system and is using the same, or similar components.
Test was performed to optimize the liquid-metal transfer and the chamber filling with the correct volume, while leaving some room for expansion.
A process for niobium coating of sliver is investi-gated. Niobium is known to provide good corro-sion resistance against liquid metals.
Thermal modelling of the target and flow analysis of the cooling geometry is under way.
15
Booi, Mlamli. "Ore sorting using microwave irradiation". Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/8336.
Abstract (sommario):
Bibliography: leaves 99-101.Automatic ore sorting machines are in common use in the mining industry. These machines generally separate valuable mineral-bearing rocks from waste rocks. At the Premier Diamond Mine in South Africa kimberlite, a diamond-bearing rock is separated from gabbro which is a waste rock. Work had been conducted previously in the Department of Electrical Engineering at the University of Cape Town to find a viable method for discriminating between gabbro and kimberlite. A technique using microwave irradiation attenuation was successful when using parallel-sided smooth-surfaced rocks. This technique used linearly polarized square antennas at 35GHz. Problems were experienced, however, with irregu1arly shaped rock s. The aim of the present study was therefore to deve1op a technique which will sort irregularly shaped rocks and eliminate the problems associated with them.
16
Mercer, Sean R. "Rock differentiation using microwave irradiation". Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/9638.
Abstract (sommario):
Includes bibliographical references.This project arose as a result of inefficiencies in the diamond recovery process at Premier Mine. A considerable amount of barren waste rock, gabbro, is mined along with the diamond bearing kimberlite. No automated method exists for separating the kimberlite from the waste rock and a device was required to effect ore sorting on a rock by rock basis. Experimentation with a microwave oven indicated that samples of kimberlite were more attenuative than samples of gabbro. The possibility of using microwave heating for rock differentiation was investigated but was impractical to implement. A study of low power microwave attenuation and reflection measurements was undertaken. Reflection measurements were found to be impractical due to the similar amounts of reflected signal from the different rock types. Microwave signal attenuation through rock samples was studied over a broad frequency spectrum. A detectable difference in signal attenuation was found through the gabbro and kimberlite. The difference in signal attenuation increased with increasing frequency. Different techniques to implement signal attenuation measurements through rock samples were investigated. The passing of rock samples through waveguide structures was found to be impractical in this application. Microwave signal attenuation measurements were successful when rock samples were placed between a transmitting and a receiving antenna. Equipment was designed and constructed with an operating frequency of 35GHz chosen due to the small antenna aperture area and the large attenuation difference at this frequency. Static measurements with this equipment revealed the problems with signal scattering and reflection from some irregularly shaped samples of low loss gabbro. The importance of these phenomenon could only be gauged from dynamic measurements. Dynamic measurements were performed using a laboratory test system with a conveyor belt capable of moving at speeds of up to 5 m/s. It was found that 93% of the kimberlite could be correctly detected whilst rejecting 67% of the gabbro. The system functioned satisfactorily and led to the filing of several patents.
17
Réjasse, Barbara. "Biocatalyse sous irradiation micro-ondes". La Rochelle, 2005. http://www.theses.fr/2005LAROS141.
Abstract (sommario):
Dans cette étude, nous avons utilisé l'irradiation micro-ondes comme source d'énergie pour réaliser différentes biosynthèses catalysées par des β-galactosidases ou la lipase B de Candida antarctica. L'influence de ce mode de chauffage alternatif sur l'activité et la stabilité enzymatiques est étudiée. Trois types de milieux réactionnels (aqueux fortement concentré en substrat, sans solvant et avec solvant organique) sont testés pour la mise en œuvre de biocatalyseurs sous irradiation micro-ondes. Dans chaque cas, le profil réactionnel obtenu est comparé à celui observé sous chauffage classique par convection, à la même température macroscopique. En milieux aqueux, nous avons étudié la biosynthèse de galacto-oligosaccharides à 40°C par transgalactosidation. La vitesse initiale de la réaction, son équilibre, ainsi que la réaction d'hydrolyse secondaire sont identiques sous irradiation micro-ondes et chauffage classique. En milieu organique, l'alcoolyse du butyrate d'éthyle par le butanol, catalysée par la lipase B de Candida antarctica, sous forme libre et immobilisée, est étudiée en système sans solvant et dans différents solvants de logP compris entre -0,15 et 3,29. En système sans solvant, de 40 à 100°C, le mode de chauffage n'a pas d'influence sur la vitesse initiale et l'équilibre de la réaction d'alcoolyse. Dans le système avec solvant, la vitesse initiale de la réaction augmente d'un facteur 1,8 sous irradiation micro-ondes, tandis que le même équilibre réactionnel est obtenu sous les deux modes de chauffage. Le facteur d'accélération de la réaction, sous irradiation, semble ne pas dépendre de la polarité du solvant utilisé. La stabilité de la lipase, en stockage dans le butanol ou le butyrate d'éthyle, est influencée par le mode de chauffage. Le processus d'inactivation enzymatique peut être ralenti ou accéléré dans le champ électromagnétique, en fonction de la température d'incubationIn this study, we have used the microwave irradiation as energy source to carry out various biosynthesis catalysed by β-galactosidases or Candida antarctica lipase B. The influence of this alternative heating mode on the enzymatic activity and stability is studied. Three types of reactional media (aqueous highly concentrated in substrates, without solvent and with organic solvent) are tested for the implementation of biocatalysts under microwave irradiation. In each case, the reactional profile obtained is compared with that observed under traditional heating (convection), at the same macroscopic temperature. In aqueous medium, a transgalactosidation reaction is studied at 40°C. The initial rate of reaction, the reactional equilibrium and the rate of secondary hydrolysis are identical under both heating modes. In organic medium, the alcoholysis of ethyl butyrate and butanol catalyzed by Candida antarctica lipase B (free and immobilized form) is studied in a solvent free system and in various solvents (logP ranging between -0,15 and 3,29). In solvent free system, the heating mode doesn't have any effect on the initial rate and reactional equilibrium of the alcoholysis, from 40 to 100°C. In solvent system, the initial rate of the reaction increases by an 1,8-factor under microwave irradiation, while identical reactional equilibrium is obtained under both heating modes. The acceleration factor of the reaction under irradiation seems not to depend on the solvent polarity. The lipase stability in storage in butanol or ethyl butyrate is influenced by the heating mode. The process of enzymatic inactivation can be slowed down or accelerated in the electromagnetic field, according to the temperature of incubation
18
Ono, Yuka. "Dosimetric advantages afforded by a new irradiation technique, Dynamic WaveArc, used for accelerated partial breast irradiation". Kyoto University, 2020. http://hdl.handle.net/2433/253145.
19
Giamarchi, Philippe. "Contribution à l'analyse des produits de radiolyse des lipides : applications en agro-alimentaire". Aix-Marseille 3, 1993. http://www.theses.fr/1993AIX30024.
Abstract (sommario):
L'etude des composes de radiolyse des lipides presente un interet particulier du fait qu'elle peut conduire a la detection et a la quantification de l'ionisation des produits (alimentaires ou non) riches en lipides. Ce travail porte sur l'identification et le dosage des hydrocarbures radioinduits; ces composes sont analyses grace a un systeme d'espace de tete dynamique suivi d'une chromatographie en phase gazeuse. La mise au point des conditions d'analyse a ete realisee en utilisant la methodologie de la recherche experimentale. La conservation des hydrocarbures radioinduits a ete etudie en s'attachant notamment a l'ajout d'antioxydants. Une etude des risques d'interference en particulier lors de la thermolyse a ete menee. Enfin, on a pu montrer que leur teneur augmente lineairement avec la dose d'ionisation. Ce travail a constitue la base de l'elaboration d'un test permettant d'une part d'identifier les produits ionises, d'autre part de quantifier la dose d'ionisation. La limite de detection atteinte dans le cas des huiles vegetales est de 0,1 kgy. Enfin, cette technique a ete appliquee sur l'avocat, pour lequel la limite de detection est de 0,5 kgy
20
Quentin, Alexis. "Modifications structurales de spinelles sous irradiation". Phd thesis, Université de Caen, 2010. http://tel.archives-ouvertes.fr/tel-00549397.
Abstract (sommario):
Ce travail concerne l'étude de matériaux de structure spinelle sous irradiations. Pour cela, des échantillons de ZnAl2O4 polycristallins et MgAl2O4 monocristallins ont été irradiés par différents ions lourds de hautes énergies. Les échantillons de ZnAl2O4 ont été étudiés par microscopie électronique en transmission ainsi que par diffraction des rayons X en incidence rasante et analyse Rietveld. Les échantillons de MgAl2O4 ont été étudiés en spectroscopie optique. Les résultats concernent principalement l'amorphisation et les modifications de la structure cristalline de ZnAl2O4, notamment l'inversion. Nous avons pu déterminer un seuil en pouvoir d'arrêt pour l'amorphisation, compris entre 11 keV/nm et 12 keV/nm, ainsi que la cinétique d'amorphisation, qui est une cinétique à multiples impacts. Nous avons étudiés par MET l'évolution de la fraction amorphe et avons mis en évidence un phénomène de nanopatterning. Concernant l'inversion, nous avons pu déterminer qu'elle se faisait via un processus d'impact unique, et que sa valeur à saturation n'atteignait pas celle d'une répartition aléatoire des cations. L'inversion et l'amorphisation possèdent des seuils de déclenchement en pouvoir d'arrêt différents, bien que très proches. L'amorphisation semble cependant être conditionnée par un préendommagement du matériau qui se traduit également par une inversion.
21
Bauer, Cletus P. "Electron irradiation n type cadmium telluride". Thesis, Monterey, California. Naval Postgraduate School, 1985. http://hdl.handle.net/10945/21306.
22
Ogilvy-Stuart, Amanda Lesley. "Endocrine sequelae of irradiation in childhood". Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296367.
23
Titapiwatanakun, V. "Pharmaceutical applications of CO2 laser irradiation". Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1474179/.
Abstract (sommario):
In the pharmaceutical development pipeline, most drugs are poorly soluble; therefore, it is important to tackle this problem by applying novel drug delivery systems or alter the drug substances with either chemical or physical modification such as amorphous formation, co-crystal formation or solid dispersion system to yield better dissolution, absorption and thus therapeutic efficacy. Applying technologies from other fields to develop such systems could be advantageous. Carbon dioxide (CO2) laser irradiation causes rapid melting and vapourization of materials through the absorption of infrared energy from a laser beam. The aim of this work was to investigate the potential pharmaceutical applications of CO2 laser irradiation in several areas including drug delivery systems, drug substances and mixtures of drug and polymer. CO2 laser irradiation was successfully utilized for three main pharmaceutical systems. Firstly, modifying drug release of irradiated enteric coated tablets (Eudragit®L100-55, L30D-55 and HPMCAS-MF) targeting to the duodenum gave rise to both fast and delayed release in pH 5.6 phosphate buffer resembling the duodenum. These changes were caused by pore formation and the change in wettability on the surface of the irradiated coat. Cast films were used to examine the physicochemical and mechanical changes and were shown to have different mechanical properties, contact angles and wettability upon high irradiation. Secondly, a proof-of-concept study of pharmaceutical co-crystal production upon irradiation at certain energy (S50P50) from a mixture of specific stoichiometric ratio of dry powders was presented through rapid melting, sublimation and vapour crystallization. Furthermore, the CO2 laser can induce the physical conversion to amorphous state of the drug-alone system (classic indomethacin) and to many physical states of the various ratios of the drug (paracetamol) and polymer (polyvinylpyrrolidone K 30) mixtures upon rapid heating process. These were clearly confirmed by a range of analytical techniques and physical stability studies. The effect of underlying process settings, namely, laser power, scanning speed, irradiation area, resolution, working distance and scale-up on production were performed.
24
Schuller, Bradley W. "Selective irradiation of the vascular endothelium". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/44787.
Abstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2007."September 2007."
Includes bibliographical references.
We developed a unique methodology to selectively irradiate the vascular endothelium in vivo to better understand the role of vascular damage in causing normal tissue radiation side-effects.The relationship between vascular endothelial cell apoptosis and intestinal crypt stem cell death was evaluated using uniform whole-body and selective vascular irradiation techniques. Mice received whole-body epithermal neutron beam irradiation. Additional dose was selectively targeted to endothelial cells from the short-ranged (5-9 [mu]m) particles released from neutron capture reactions in 10B confined to the blood by incorporation into 70-90 nm-diameter liposomes. Mice also received uniform photon doses above and below the threshold for death from the gastrointestinal (GI) syndrome. When plotted versus neutron beam dose, the crypt microcolony assay showed the same dose response for both the neutron beam-only and neutron beam plus boronated liposome groups. The added dose selectively delivered to the microvasculature did not cause any additional crypt loss. Jejunal cross-sections were prepared 4 hrs after irradiation and stained with TUNEL to observe and score apoptotic cells in the villus lamina propria. To uniquely identify the type of cell undergoing apoptosis in the lamina propria, intestinal specimens from various mice in the TUNEL studies were sectioned and stained with Meca-32 to identify endothelial cells and caspase-3 to identify apoptotic cells and visualized using dual-fluorescence microscopy. The TUNEL data showed a low level (~2 apoptotic cells per villus) of apoptosis in the lamina propria for both the uniform (photon or neutron) and selective vascular irradiation conditions that was independent of the administered dose.
(cont.) The dual-fluorescence studies indicated that most apoptotic bodies in the lamina propria were not endothelial cells but, rather, apoptotic leukocytes. These data demonstrate that there is no causal relationship between vascular endothelial cell apoptosis and crypt stem cell death in the mouse small intestine.
by Bradley W. Schuller.
Ph.D.
25
Holtom, Philip Derek. "Irradiation studies of astrophysical ice analogues". Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1444790/.
Abstract (sommario):
In this thesis the formation of molecular species in cold icy mantles, typical of those in the interstellar medium (ISM) has been studied. The construction of an ultra high vacuum system for the formation and containment of these astrophysical ice analogues is described. The method of preparation of these ices is detailed and analysis methodologies are discussed. VUV spectra of molecular ices (e.g. SO2, CH3NH2, OCS) measured on the UV1 beam line of the Astrid Synchrotron facility at the University of Aarhus in Denmark, are presented. Molecular synthesis (e.g. CO3, CO, H2CO3) induced by ion irradiated CO2/H 2O ices using facilities at Queens University Belfast are also reported. In particular this thesis focuses on the irradiation studies of the binary ice mixture of Methylamine (CH3NH2) and Carbon Dioxide (CO2). The results of irradiation of CH3NH2 and CO2 binary ice mixtures by ultraviolet photons, and electrons are presented. The apparent production of the amino acid - glycine - in our irradiated samples is discussed together with possible production processes.
26
Sobie, Cameron. "Prediction of irradiation hardening in metals". Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54963.
Abstract (sommario):
The purpose of this thesis is to improve predictions of irradiation hardening in metals with a focus on coarse-graining via meso-scale simulations. Increasing hardness and decreasing in ductility in nuclear reactor pressure vessel steel is the limiting factor of nuclear reactor life, and accurately predicting reactor life is of the utmost importance for the safe operation of nuclear facilities. This is an inherently multi-scale problem with primary damage occurring at the atomic scale and its effects propagating across ten orders of magnitude in length and time scale to changes in macroscopic material properties, which must be reflected in its methods of prediction.
To achieve this goal, this thesis develops two novel approaches to simulate the motion of dislocations in irradiated alpha-iron. First, a dislocation dynamics simulation coarse-graining insight from atomistic dislocation-defect simulations is used to guide the selection of proposed constitutive models. Several studies investigating the effect of size distribution show that the mean defect size can be used with the selected models to predict material hardening without a complex treatment for the defect size distribution. The hardening effect of the commonly observed defect types are found independently and a superposition principle is proposed for materials with both defect types. Second, a link to transition state theory and thermally activated reactions is established using a new method augmenting a discrete dislocation dynamics simulations with the nudged elastic band method to characterise the minimum energy pathways of dislocation reactions. This development enables calculations of activation energy for dislocation events using a continuum method as well as the numerical calculations of dislocation attempt frequency. The thesis concludes with an extension to the analysis of coarse-graining unit events to large scale dislocation-obstacle bypass phenomena.
27
Hanif, Imran. "Ion irradiation modification of silicon nanowires". Thesis, University of Huddersfield, 2017. http://eprints.hud.ac.uk/id/eprint/32630/.
Abstract (sommario):
Ion irradiation modification of silicon nanowires has been explored in-situ using the Microscope and Ion Accelerator for Materials Investigations (MIAMI) facility at the University of Huddersfield. Ion irradiation experiments were designed using the Stopping and Range of Ions in Matter (SRIM) Monte Carlo computer code. A multislice SRIM method was developed to estimate the damage and ion implantation in a nanowires geometry and a code was developed to incorporate SRIM into MatLab. In-situ Transmission Electron Microscopy (TEM) has been used to explore the ion-beam-induced bending of silicon nanowires under different irradiation conditions and the underlying mechanisms which drive nanowire bending have been identified. Furthermore, a tipping point for direction reversal of bending under different irradiation conditions has been identified. Recrystallisation of silicon nanowires was also investigated using thermal annealing. The effects of 7 keV Xe+ ions on silicon nanowires have been investigated under industrial processing conditions. Structural and morphological changes of silicon nanowires have been observed. These include nanowire bending, amorphisation, bubble formation and sputtering. The depth of damage has also been measured experimentally and was compared with the predictive damage using SRIM. In order to calculate the temperature along a nanowire during an in-situ TEM heating experiment, the relevant parameters have been found from the literature which will be used to set up a finite element model. Atomic Force Microscopy (AFM) was used to measure the surface roughness of silicon nanowires and molybdenum grids. Other parameters of interest include the Hamaker’s constant for the Van der Waals forces as well as the Young’s modulus, thermal conductivity and specific heat capacity of silicon nanowires and the ultra-thin oxide layer on their surface.
28
Sibuyi, Praise. "Irradiation induced effects on 6h-SIC". University of the Western Cape, 2012. http://hdl.handle.net/11394/8467.
Abstract (sommario):
Philosophiae Doctor - PhDThe framework agreement in the year 2000 by the international community to launch Generation IV program with 10 nations, to develop safe and reliable nuclear reactors gave rise to the increased interest in the studies of SiC and the effect of different irradiations on solids. Silicon carbide is a preferred candidate used in harsh environments due to its excellent properties such as high chemical stability and strong mechanical strength. The PBMR technology promises to be the safest of all nuclear technology that have been developed before. SiC has been considered one candidate material being used in the fabrication of pebble bed fuel cell. Its outstanding physical and chemical properties even at high temperatures render it a material of choice for the future nuclear industry as whole and PBMR in particular. Due to the hostile environment created during the normal reactor operation, some of these excellent properties are compromised. In order to use this material in such conditions, it should have at least a near perfect crystal lattice to prevent defects that could compromise its strength and performance. A proper knowledge of the behavior of radiation-induced defects in SiC is vital. During irradiation, a disordered crystal lattice occurs, resulting in the production of defects in the lattice. These defects lead to the degradation of these excellent properties of a particular material. This thesis investigates the effects of various radiation effects to 6H-SiC. We have investigated the effects of radiation induced damages to SiC, with a description of the beds and the importance of the stability of the SiC-C interface upon the effects of radiations (y-rays, hot neutrons). The irradiated samples of 6H-SiC have been studied with various spectroscopic and structural characterization methods. The surface sensitive techniques such as Raman spectroscopy, UV-Vis, Photoluminescence and Atomic Force Microscopy will be employed in several complimentary ways to probe the effect of irradiation on SiC. The obtained results are discussed in details.
29
Rana, Aman. "Optimizing Weed Management via Microwave Irradiation". Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/75115.
Abstract (sommario):
One potential alternative to chemical weed control is the use of microwave radiation, a particular form of indirect thermal weeding. Absorption of microwave radiation causes water molecules within the tissue to oscillate, thereby converting electromagnetic energy into heat. This technique is rapid, versatile and effective, as the electromagnetic waves heat the plant tissue and destroy cellular integrity. The objective of this research was to evaluate the potential use of dielectric heating for weed management. Ten weed species representing monocots and dicots were selected for this study: southern crabgrass, dallisgrass, yellow nutsedge, fragrant flatsedge, false green kyllinga, common ragweed, field bindweed, henbit, white clover, and pitted morningglory. There was a lag or warm up period between energizing the magnetron and actual microwave radiation production. To eliminate the gap between electric power supplied to magnetron and actual microwave radiation produced, a conveyer was used. Overall injury to grasses, sedges and broadleaf weeds was higher at each dose when weeds were treated by microwave radiation while moving on a conveyer in comparison to being stationary. Grasses showed slightly more tolerance to microwave treatments in comparison to broadleaf weeds. Older weeds (8 to 10 weeks old) showed more tolerance to microwave treatments in comparison to younger weed plants (4 to 6 weeks old). Microwave radiation was able to control a range of weed species, although larger weeds were more likely to regrow after treatment. Ambient temperature had a significant effect on injuries caused by microwave radiation to target weeds, with control increasing as the air temperature increased. Weed control using microwave radiation required more energy when weeds were treated at 13 C compared to 35 C. More energy was needed at lower air temperatures to raise the plant canopy temperature from ambient levels to beyond the biological limit. Microwave radiation at lower doses caused greater injury to common chickweed and yellow woodsorrel than bermudagrass, suggesting the potential for selective weed control in certain situations. A custom built microwave applicator provided similar control of emerged weeds as the contact herbicides diquat and acetic acid.Ph. D.
30
Torchy, Séverine. "Transfert d'hydrogène sous irradiation micro-ondes". Lille 1, 2000. http://www.theses.fr/2000LIL10069.
Abstract (sommario):
Cette étude concerne les réactions de transfert d'hydrogène sous irradiation micro-ondes, utilisant comme agents de transfert des molécules organiques telles que l'acide formique, les dihydropyridines et les alcoolates d'aluminium. L'aspect physique de l'irradiation micro-ondes, ses répercussions sur la matière, et les applications possibles en synthèse organique sont résumés. Une deuxième partie étudie la N-méthylation (la N,N-diméthylation) d'amines secondaires (primaires) par le méthanal en présence d'acide formique. La réaction est généralement réalisée sans solvant, un net effet micro-ondes est mis en évidence. Cet accès aisé à des amines tertiaires conduit ensuite à étudier le comportement des sels d'ammonium qui en dérivent dans les conditions de transposition de Stevens ou Sommelet-Hauser : l'irradiation micro-ondes accélère ces réarrangements. Les deux réactions quaternarisation-transposition peuvent s'opérer en une seule étape (réaction tandem). Une quatrième partie concerne la synthèse de dihydropyridines et leur utilisation comme agents de réduction d'alcènes désactivés. Les dihydropyridines non substituées en 4 se prêtent aisément à un transfert d'hydrogène : les pyridines et les alcanes résultants sont préparés en une seule étape. Les deux derniers chapîtres concernent l'utilisation d'alcoolates d'aluminium dans la réduction des dérivés carbonylés (5ʿ partie) et la réaction inverse, l'oxydation d'alcools (6ʿ partie). La réduction s'opère aisément avec des résultats très satisfaisants. L'oxydation est plus délicate à mettre en œuvre.
31
AKAMATSU, JOUSSET MARIELLE. "Evolution structurale d'alliages ferritiques sous irradiation". Paris 11, 1994. http://www.theses.fr/1994PA112007.
Abstract (sommario):
Nous avons etudie l'evolution, sous l'effet de l'irradiation, de la microstructure et des proprietes mecaniques d'alliages ferritiques modele (fe-cu) et d'aciers de cuve de reacteur nucleaire a eau pressurisee (chooz a). Trois traitements de precipitation sont compares: vieillissement thermique a 500c, irradiation aux electrons (3mev, 290c) et irradiation aux neutrons (290c). L'utilisation conjointe de la sonde atomique et de la diffusion des neutrons aux petits angles a permis d'obtenir les caracteristiques (taille, densite numerique, composition) des precipites formes a l'echelle nanometrique, en fonction du temps ou de la fluence. Dans les alliages fe-cu (0 a 1,4% poids) irradies, les precipites ne sont pas constitues de cuivre pur (comme le prevoirait le diagramme de phase), mais contiennent une forte proportion de fer et de lacunes. Les mesures de durete sous faible charge montrent un net durcissement du a ces precipites. Les irradiations conduisent a un durcissement superieur a celui du au vieillissement thermique, du fait de la creation de nombreux defauts ponctuels. Nous avons essaye d'analyser nos resultats dans les termes du modele durcissement par effet de module de russel et brown. Nos tentatives d'evaluation non destructive par mesure du bruit barkhausen revelent simplement que les precipites formes par irradiation sont vraisemblablement trop petits pour etre detectes. Dans l'acier de cuve, l'irradiation aux neutrons en service a conduit a la formation de nuages d'atomes de ni, mn, si et cu au sein de la matrice de fer
32
Quentin, Alexis. "Modifications structurales de spinelle sous irradiation". Caen, 2010. http://www.theses.fr/2010CAEN2059.
Abstract (sommario):
Ce travail concerne l'étude de matériaux de structure spinelle sous irradiations. Pour cela, des échantillons de ZnAl2O4 polycristallins et MgAl2O4 monocristallins ont été irradiés par différents ions lourds de hautes énergies. Les échantillons de ZnAl2O4 ont été étudiés par microscopie électronique en transmission ainsi que par diffraction des rayons X en incidence rasante et analyse Rietveld. Les échantillons de MgAl2O4 ont été étudiés en spectroscopie optique. Les résultats concernent principalement l'amorphisation et les modifications de la structure cristalline de ZnAl2O4, notamment l'inversion. Nous avons pu déterminer un seuil en pouvoir d'arrêt pour l'amorphisation, compris entre 11 keV/nm et 12 keV/nm, ainsi que la cinétique d'amorphisation, qui est une cinétique à multiples impacts. Nous avons étudiés par MET l’évolution de la fraction amorphe et avons mis en évidence un phénomène de nanopatterning. Concernant l'inversion, nous avons pu déterminer qu'elle se faisait via un processus d’impact unique, et que sa valeur à saturation n'atteignait pas celle d'une répartition aléatoire des cations. L'inversion et l'amorphisation possèdent des seuils de déclenchement en pouvoir d'arrêt différents, bien que très proches. L’amorphisation semble cependant être conditionnée par un pré-endommagement du matériau qui se traduit également par une inversionThis work is devoted to the study of spinel structure materials under radiation. For that purpose, samples of polycrystalline ZnAl2O4 and monocrystalline MgAl2O4 were irradiated by different heavy ions with different energies. Samples of ZnAl2O4 were studied par electron transmission microscopy, and by grazing incidence X-Ray diffraction and Rietveld analysis. Samples of MgAl2O4 were studied by optical spectroscopy. Most of the results concern amorphisation and crystalline structure modification of ZnAl2O4 especially the inversion. We were able to determine a stopping power threshold for amorphisation, between 11 keV/nm and 12 keV/nm, and also the amorphisation process, which is a multiple impacts process. We studied the evolution of the amorphous phase by TEM and showed a nanopatterning phenomenon. Concerning the inversion, we determined that it did happen by a single impact process, and the saturation value did not reach the random cation distribution value. Inversion and amorphisation have different, but close, stopping power threshold. However, amorphisation seems to be conditioned by a predamage of the material which consists in inversion
33
Hu, Rong. "Irradiation effects on Fe-Cr alloys". Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.560928.
Abstract (sommario):
Ferritic chromium steels are important structural materials for future nuclear fission and fusion reactors due to their advantages over traditional austenitic steels, including low swelling rates, better thermal fatigue resistance, and lower thermal expansion coefficients. Radiation-induced segregation or depletion (RIS/RID) of solute atoms at grain boundaries is considered to be a potentially significant phenomenon for structural materials because of its potentially detrimental role in affecting microstructure and furthermore mechanical properties. However, the behaviour of Cr at grain boundaries in ferritic steels is not well understood. Both segregation and depletion of Cr at grain boundary under irradiation have been previously observed and no clear dependency on irradiation condition or alloy type has been presented. Furthermore, ferritic alloys are known to undergo hardening and embrittlement after thermal aging in the temperature range of 300-550DC and this phenomenon is related with a and a' phase separation occurring in the solid solution. However the low temperature a-a' miscibility gap in the currently used phase diagram is extrapolated from high temperature results and conflicts with many experimental observations. To understand the Cr behaviour at gram boundaries in ferritic steels under irradiation, a systematic approach combining SEM/EBSD, FIB specimen preparation and APT analysis has been developed and successfully applied to a Fe- 15.2at%Cr to investigate the effect of pre-irradiation chemistry, grain boundary misorientation, impurities, irradiation damage, irradiation depth, and other possible factors to get a better understanding of RIS/RID phenomena. Both low sigma boundaries and randomly selected high angle boundaries have been investigated in detail. Systematic differences between the behaviour of different classes of boundaries had been observed, and the operating mechanisms are also discussed in this thesis. The maximum separation method has been applied on APT data to study the C- enriched clusters and Cr-enriched clusters, which were not directly visible on the atom maps. The composition of the Cr-enriched clusters was consistent with a' phase and the irradiation was found to accelerate the nucleation rather than the growth of these clusters. Such results provided important information in re- determining the a-a' phase boundary.
34
Le, Gac Alexandre. "Comportement sous irradiation des verres d'aluminosilicate". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX047/document.
Abstract (sommario):
La compréhension des effets d’irradiation dans les verres d’oxyde est importante dans le domaine du conditionnement des déchets nucléaire et requière l’évaluation du rôle des formateurs de réseau, principalement le silicium, le bore et l’aluminium, mais aussi du rôle des éléments alcalins et alcalino-terreux qui peuvent agir en tant que modificateurs de réseau ou compensateurs de charge. Les verres d’aluminoborosilicates ont été très étudiés et le rôle des changements de coordinence du bore sur l’évolution structurale du verre sous irradiation a été souligné. Cependant, il n’y a que peu d’études sur les verres d’aluminosilicates et presque qu’aucune information sur l’influence de l’aluminium et de ses compensateurs de charge sur l’évolution du réseau sous irradiation. Ce travail de thèse a donc pour objectif de déterminer les effets de la teneur en aluminium et du type de compensateurs de charge (ici les ions sodium et calcium) sur l’évolution de la structure des verres d’aluminosilicates sous irradiation. Afin de comprendre les différents phénomènes dans les verres d’oxyde complexes, 13 verres simplifiés, composés d’oxydes de SiO2, Al2O3, Na2O et CaO, ont été élaborés. Ainsi, l’influence des rapports Na2O/CaO et Al2O3/SiO2 et de la teneur en Al2O3 ont été investigués. Pour simuler les désintégrations alpha et comparer les dommages électronique et balistique, des irradiations externes aux ions He2+ d’énergie 5 MeV et aux ions Au4+ d’énergie 7 MeV ont été réalisées sur les verres. Des irradiations aux électrons ont également été faites afin d’obtenir des échantillons irradiés en volume par des collisions électroniques à faible pouvoir d’arrêtThe understanding of radiation effects in oxide glasses is important in nuclear waste conditioning field and requires the evaluation of the role of the glass formers, mainly silicon, boron and aluminum, but also of the alkali and alkali-earth elements that can act either as modifier elements or charge compensators. Aluminoborosilicate glasses were highly studied and the role of boron coordination changes on structural evolution under irradiation was highlighted. However, there are only few studies on aluminosilicate glasses and almost no information about the influence of aluminum and its charge compensators on the glassy network evolution under irradiation. The goal of this work is therefore to determine the effects of aluminum content and type of charge compensators (here, Na and Ca cations) on the aluminosilicate glass structure evolution under irradiation. To understand the different phenomena in complex oxide glasses, 13 simplified glasses, composed of SiO2, Al2O3, Na2O and CaO oxides, were elaborated. Hence, the influence of Na2O/CaO and Al2O3/SiO2 ratios, and Al2O3 content, were investigated. To simulate alpha decays and compare electronic and ballistic damage, external irradiations at room temperature with 5 MeV He2+ and 7 MeV Au4+ were performed on glasses. 2.5 MeV electron irradiations were also done to obtain bulk samples irradiated by electronic collisions at low stopping power
35
Mangiacotti, M. "DETERMINATION OF IRRADIATION MARKERS IN FOODS". Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/232733.
Abstract (sommario):
Today’s food industry is faced with several important challenges, including food product deterioration and the constant increase of diseases related to the presence of pathogenic microorganisms in food products. Thus, adequate and effective food preservation strategies are even more important. Food irradiation is a technological process that can improve the microbiological quality of foodstuffs and extend the period in which it can be safely consumed. The radiation treatment, carried out under conditions of Good Manufacturing Practice, is considered as an effective, widely applicable food processing method judged to be safe on extensive available evidence. This technology can reduce the risk of food poisoning, control food spoilage and extend the shelf-life of foods without detriment to health and with minimal effect on nutritional or sensory quality. Due to its numerous positive effects, including those of a commercial nature, food irradiation has assumed a highly important role in the field of food preservation, and increasingly large numbers of foodstuffs are subjected to this treatment each year. For some time now, countries equipped with adequate food irradiation facilities have used this technology at well defined doses for the preservation of various foodstuffs. Because of the divergent opinions expressed by many consumers' organizations, the European Union has issued two directives (1999/2/EC and 1999/3/EC), which have been implemented in Italy by Legislative Decree No. 94 of 30 January 2001. Those directives aims at harmonizing the rules concerning the treatment and trade of irradiated foods in EU countries. With the open market, each country is obliged to accommodate the presence in its internal market of irradiated food commodities treated in other EU states or in extra-European countries. To further safeguard the consumer, the EU legislation provides for official annual checks at the product marketing stage, with the purpose of identifying improperly labeled or unauthorized products. Thus far, only limited food categories has been studied and subjected to interlaboratory validation by analytical detection methods for irradiated food identification. To meet the specific requirements of the laws and to increase acceptance of this type of food preservation technology, we have extended the field of application of both screening (PSL) and confirmatory (ESR, TL) physical methods to check compliance with labeling of irradiated foodstuffs. Therefore for consumer protection and information, following the invitation from the European Commission to improve and develop more reliable analytical standards, research work was focused on new applications of these physical methods. Relevant contributions have been made to the extension of the current field of application, with the development of promising analytical procedure able to estimate the actual dose administered to treated foods. The first goal was achieved investigating, even at low doses (0.1 kGy), the luminescence yield of oysters, considered a great delicacy in many parts of the world, and validating its identification with two physical techniques: PSL as screening method and TL as a confirmatory one. Besides oysters other seafood, including bivalve mollusks, i.e. brown Venus shells, clams, and mussels, all of which are widely consumed and likely to be treated with irradiation were studied with Electron Spin Resonance (ESR) spectroscopy.
It is well known that irradiation by ionising radiation leads to the formation of many radical species which, if stable, could be detected in calcified tissue such as mollusks' shell. Identification of four irradiated species of bivalve mollusks, i.e. brown Venus shells (Callista chione), clams (Tapes semidecussatus), mussels (Mytilus galloprovincialis) and oysters (Ostrea edulis) was performed. ESR could definitely identify irradiated seashells due to the presence of long-lived free radicals, primarily CO2-, CO33-, SO2- and SO3- radical anions. The presence of other organic free radicals, believed to originate from conchiolin, a scleroprotein present in the shells, was also ascertained. The use of one of these radicals as a marker for irradiation of brown Venus shells and clams can be envisaged. In addition to detection procedures a reliable dosimetric protocol for the reconstruction of the administered dose in irradiated oysters was proposed. Finally the results of a study on official checks by an accredited laboratory aimed at both evaluating the performances of detection methods and the presence of irradiated food on the Italian market, are discussed. Non-compliances found are due to both incorrect labelling and irradiation in non approved facilities in extra European countries. In summary, two physical methods, electron spin resonance (ESR) spectroscopy and thermoluminescence (TL) were studied most extensively and applied on a wide range of foods with successful results, whereas limitations of current standards were also assessed. The development and application of analytical methods for correct identification of irradiated samples from non-irradiated samples, along with protocols for dose evaluation, have become important for several purposes: upholding regulatory controls, checking compliance against labeling requirements, facilitating international trade, and reinforcing consumer confidence. Therefore the research on new detection methods represents a key area and more studies in this field should be encouraged.
36
Pellegrino, Stéphanie. "Irradiation aux ions des carbures ZrC et TiC. Effets des pertes d'énergie électronique et nucléaire". Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS018/document.
Abstract (sommario):
Cette étude est orientée sur les céramiques réfractaires des métaux de transition, comme le carbure de titane et de zirconium, envisagées pour leurs caractéristiques de résistance en conditions extrêmes. Ces céramiques seraient soumises à différentes sources d'irradiation (les neutrons, les produits de fission, les désintégrations alpha) dans les futurs réacteurs de génération IV. Les rayonnements rencontrés en réacteur peuvent être simulés par des irradiations externes à l'aide d'accélérateurs de particules, en utilisant des ions variés dans une large gamme d'énergie. Ces instruments permettent de reproduire en conditions contrôlées l'endommagement subi par des les matériaux internes aux centrales nucléaires.Dans un tel contexte radiatif, deux processus majeurs gouvernent l'endommagement des matériaux: les collisions nucléaires induites par les irradiations avec des ions de faible énergie (comme les noyaux de recul) et les excitations électroniques intervenant dans les irradiations avec des ions de grande énergie (comme les produits de fission). La prédominance de l'un ou de l'autre de ces processus est reliée à la masse et à l'énergie de la particule accélérée. Pour comprendre la contribution de chaque effet dans les mécanismes d'endommagement des structures cristallines soumises à des irradiations, nous avons simulé des rayonnements impliquant, d'une part, des ions de basse énergie, i.e. de quelques MeV et, d'autre part, des ions de grande énergie, i.e. de quelques centaines de MeV. Les principaux objectifs de ce travail ont été: (i) d'étudier le comportement de ces deux carbures sous irradiation, (ii) de déterminer les modifications structurales, chimiques et mécaniques induites par les effets nucléaires et électroniques, (iii) de comprendre les mécanismes d'endommagement dans ces carbures dans le régime nucléaire et (iv) d'essayer d'expliquer les résultats expérimentaux par les calculs obtenus en simulation.Pour cela, différentes techniques de caractérisation ont été combinées afin d'expliquer le scénario de ces carbures sous irradiation avec comme référence, le carbure de silicium SiC très étudié par le passé. Ces techniques complémentaires sont: la spectrométrie de rétrodiffusion de Rutherford en mode canalisé (RBS-C), la diffraction des rayons X (DRX), la spectroscopie Raman, la microscopie électronique en transmission (MET) et la nanoindentation. La combinaison de ces techniques expérimentales ainsi que la simulation a permis de conforter nos résultats et les différentes hypothèses formulées. Nous avons pu établir ainsi un scénario pour ces deux types de carbures TiC et ZrC sous irradiation aux ionsThis study is focused on the ceramic refractory transition metals, such as titanium carbide and zirconium envisaged to their strength characteristics under extreme conditions. These ceramics are subject to various sources of radiation (neutrons, fission products, the alpha decays) in future generation reactors IV. Radiation encountered in the reactor can be simulated by external irradiation with particle accelerators, using various ions in a wide energy range. These instruments can reproduce in controlled conditions damage suffered by nuclear materials.In such radiative context, two major processes govern damages into the materials: nuclear collisions induced by irradiation with low energy ions (like the recoil nuclei) and electronic excitations involved in irradiation with high-energy ions (such as fission products). The predominance of one of these processes is connected to the mass and energy of the accelerated particle. To understand the contribution of each effect in the damage mechanisms of crystal structures subjected to irradiation, we simulated radiation involving, on the one hand, low energy ions, i.e. a few MeV and, secondly, high energy ions, i.e. a few hundred MeV. The main objectives of this work were: (i) to study the behavior of these two carbides under irradiation, (ii) determine the structural, chemical and mechanical changes induced by nuclear and electronic effects, (iii) understand the damage mechanisms in these carbides in the nuclear regime and (iv) to try to explain the experimental results obtained by simulation calculations.For this, various characterization techniques were combined to explain the scenario of these carbides under irradiation as a reference, the silicon carbide SiC extensively studied in the past. These additional techniques are: Rutherford Backscattering Spectrometry in channeling mode (RBS-C), the X-ray diffraction (XRD), Raman spectroscopy, Transmission Electron Microscopy (TEM) and nanoindentation. The combination of these experimental techniques and simulation helped to consolidate our results and various assumptions. We were able to establish a scenario for these two types of carbides TiC and ZrC under ion irradiation
37
Dahl, Erik Monroe. "Single-Walled Carbon Nanotube Response to Neutron and Gamma Irradiation". Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/50856.
Abstract (sommario):
The unique electronic properties of single-walled carbon nanotubes (SWNTs) have sparked interest for using such nanomaterials in the nuclear industry and within radiation detection devices. To explore the application of SWNTs in the nuclear industry, it was first deemed necessary to study how SWNTs respond to the two main types of radiation occurring in nuclear environments, neutrons and gamma rays. SWNT samples were irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory with neutrons and gamma rays at incremented lengths of time allowing for multiple fluence intensities to be received by the samples. After irradiation, Raman spectroscopy was used to monitor the damage incurred from neutron and gamma irradiation. It was found that disorder within the SWNT lattice network increased with increasing irradiation intensity. The results indicated that the gamma irradiation was causing the majority of the damage with little to no damage caused by the neutron irradiation. Further investigation showed that the non-linearity of the disorder increase with increasing irradiation intensity was typical of sample doping instead of the expected particle impacts. It was concluded that the gamma irradiation was generating dopants within the SWNTs by the process of water radiolysis. Water vapor trapped between the SWNT film layer and the substrate that the film layer was placed on was identified as the source of the sample dopants. Although unexpected, the results from this experiment have provided insight into a potential gamma radiation detection technique using SWNTs that has never been considered until now.
Master of Science
38
Jutier, Frédéric. "Influence de l'auto-irradiation sur la supraconductivité de composés à base de plutonium". Paris 11, 2006. http://www.theses.fr/2006PA112115.
Abstract (sommario):
Bien que le plutonium (Pu) soit plus connu pour ses propriétés nucléaires, il est également un métal fascinant dont les électrons 5f se situent à la frontière entre un caractère itinérant et localisé. Ce comportement unique dans le tableau périodique des éléments positionne le Pu métal à un croisement dans les propriétés électroniques. La découverte récente de la supraconductivité dans PuCoGa5 et PuRhGa5 est une nouvelle preuve directe de la complexité des propriétés électroniques du plutonium. Les valeurs élevées de la température critique et du deuxième champ critique semble indiquer l'existence d'une troisième classe de supraconducteurs, transitoire entre les composés fermions lourds à base d'uranium et de cérium, et les supraconducteurs à haute température critique à base de cuprates. Les grandes valeurs des paramètres critiques associées à une densité de courant élevée donneraient à ces nouveaux matériaux un potentiel prometteur pour de futures applications technologiques, si ce n'était le caractère extrêmement radiotoxique des composés à base de plutonium. L'intérêt des composés PuCoGa5 et PuRhGa5 est la décroissance alpha du plutonium qui constitue alors une source continue d'irradiation in situ. Le vieillissement de ces composés aura donc un impact sur les paramètres critiques de la supraconductivité. Ce travail a donc porté sur l'étude par résistivité électrique et aimantation de l'évolution des paramètres de la supraconductivité en fonction du vieillissement des échantillons, pour en déduire l'influence des " impuretés " et des défauts sur leur comportement supraconducteur et déterminé des indications éventuelles d'un caractère non conventionnelAlthough plutonium (Pu) is most known for its nuclear properties, it is also a fascinating metal whose 5f electrons are at the threshold between itinerancy and localization. This unique behaviour in the periodic table makes Pu metal being at the crossover in electronic properties. The recent discovery of superconductivity in PuCoGa5 and PuRhGa5 is a new direct evidence of plutonium's electronic properties complexity. The high values of the critical temperature and the upper critical field seem to point to the existence of a third class of superconductor, transitional between uranium- and cerium-based heavy fermion systems, and the high-Tc copper oxides. If it were not for the toxicity hazards associated with plutonium compounds, and their high critical parameters together with a high critical current, would make these materials of promising potential for technological applications. The advantage of the PuCoGa5 and PuRhGa5 compounds is the alpha radioactivity of plutonium which constitutes a continuous in situ source of irradiation. The ageing of these compounds will have thus an impact on the critical parameters (Tc, Hc2, Jc). This work is based on the study by electrical resistivity and magnetisation of the evolution of the superconductivity parameters as a function of samples ageing, in order to determine the influence of “impurities” and defects on their superconducting behaviour and thus to bring eventual indications of an unconventional character
39
Fourdrin, Chloé. "Effets d'irradiation dans les argiles : applications environnementale et géologique". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00656014.
Abstract (sommario):
Les défauts d'irradiations dans les minéraux présents à la surface de la terre ont donné lieu à de nombreuses études. Parmi ces minéraux, les argiles ont des propriétés (capacité de rétention des radioéléments, gonflement...) qui les rendent utiles dans le cadre du stockage des déchets radioactifs. Afin de s'assurer de la stabilité des argiles se trouvant autour du colis de déchets, il est nécessaire d'étudier leurs propriétés physico-chimiques après irradiation. Cette thèse est séparée en trois parties qui sont axées autour de cette thématique. Dans une première partie, nous verrons quels sont les effets des rayons alpha sur la surface spécifique de la kaolinite et nous exposerons les phénomènes physique induits par ces rayonnements ionisants. La seconde partie traitera de la solubilité des smectites amorphisées dans un milieu basique et plus particulièrement de la cinétique de dissolution. Nous verrons que cette dissolution est favorisée par l'amorphisation. Enfin dans une troisième partie, nous nous sommes intéressés au géosystème analogue naturel de Nopal (Chihuahua, Mexique), où le dosimètre kaolinite peut permettre d'étudier les migrations anciennes de l'uranium au sein de la roche.
40
Lou, Yu. "Comportement des silices mésoporeuses sous irradiations ioniques". Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTT228/document.
Abstract (sommario):
Dans le cadre de la recherche de nouvelles solutions pour le traitement des effluents radioactifs, la stratégie dite « séparation – conditionnement » qui consiste à mettre en oeuvre un support poreux fonctionnalisé pour la sorption des radionucléides, qui pourrait également être un matériau précurseur pour l’élaboration d’une matrice de conditionnement, est une alternative qui présente des perspectives intéressantes. Dans ce contexte, la silice mésoporeuse est un matériau qui présente plusieurs atouts : une grande surface spécifique fonctionnalisable, une élaboration à basse température et enfin, la possibilité de confiner le radionucléide par fermeture de la porosité via l’application d’une contrainte chimique, mécanique, thermique… Au cours de ces différentes étapes, du fait de la présence de radionucléides, la structure mésoporeuse serait soumise à l’auto-irradiation, c’est pourquoi il est important de connaitre l’évolution d’une telle structure dans ces conditions.L’objectif de cette thèse était donc de comparer les comportements de différentes silices mésoporeuses sous des conditions d’irradiations variées qui donnent lieu à deux effets principaux, l’effet balistique (nucléaire) et l’effet inélastique (électronique). Pour atteindre cet objectif, les irradiations externes par des ions lourds ont été utilisées pour simuler les processus d’auto-irradiation. Les techniques de caractérisation post-irradiation (réflectivité des rayons-X, adsorption gazeuse) ont été mises en œuvre. Une compaction totale de la structure mésoporeuse a été observée en régime balistique pour une dose d’environ ~1025 eV/cm3 (~10 dpa). Lors des irradiations en régime électronique, les ions présentant un pouvoir d’arrêt inférieur à 1keV/nm n’ont pas d’effet important sur l’évolution de la structure mésoporeuse, seuls les ions présentant un pouvoir d’arrêt élevé (Ni-638 MeV, dE/dx~5 keV/nm), supérieur au seuil de formation des traces dans la silice thermique, induisent une densification de la structure. Jusqu’à une dose Eélec.=1025 eV/cm3 le phénomène de saturation n’a pas été observé. Aucune différence importante n’a été observée entre les différentes silices mésoporeuses étudiées. Ces résultats indiquent une bonne résistance de ces structures aux dommages créés par l’irradiation.L’origine de ces comportements n’a pas été clairement établie. Les effets purement thermiques des irradiations ne peuvent pas être invoqués car une étude comparative a montré les processus de densification étaient totalement différents. Une approche de modélisation par Dynamique Moléculaire classique a permis de reproduire avec succès l’effondrement des mésopores, ce qui apporte un début d’explication dans le cas de l’endommagement en régime balistique. En régime électronique, les résultats obtenus sont cohérents avec les résultats bibliographiquesIn the search of new solutions to treat radioactive effluent, the so-called “separation-conditioning” strategy, which consists of implementing a functionalized porous matrix for the radionuclide adsorption, is an interesting alternative way. Such porous matrix could even act as a long term conditioning matrix in the second step. For this purpose, mesoporous silica presents several advantages like enormous fonctionalisable surface, possibility to prepare at low temperature and pore closure which favors long term conditioning. During its working process and with the presence of radionuclide, the mesoporous structure will be exposed to self-irradiation. This is why it’s important to know the structure evolution under such conditions.The objective of this thesis is to compare different mesoporous structures under various irradiation conditions which induce two major effects, the ballistic (nuclear) effect and the inelastic (electronic) effect. In order to achieve these objectives and thanks to their several advantages, external irradiations with heavy ions were used to simulate self-irradiation processes. Adapted post-irradiation characterizations, like X-ray reflectivity and gas adsorption, were carried out. In the ballistic regime, a total compaction due to mesopore collapse is observed at a dose about ~1025 eV/cm3 (~10 dpa). In the electronic regime, ions of stopping power inferior to 1keV/nm do not present obvious effect on the mesoporous structure evolution. Only the Ni-638 MeV with stopping power ~5 keV/nm shows significant collapse effect but no total compaction was observed until the maximum studied dose about Eelec.=1025 eV/cm3. These results indicate a good resistance of these structures against irradiation damage.The origin of these structural behaviors has not been clearly understood. Thermal effect, considered as secondary irradiation effect, cannot be referred to because a comparative study showed completely different densification process. Additionally, a trial with classic Molecular Dynamics modelling for purely ballistic effects was undertaken. It allows to successfully reproduced mesopore collapse and to set foot on the explanation in case of ballistic regime. In the electronic regime, the results are compatible with literatures
41
DOUIFI, LEILA. "Detection par resonance paramagnetique electronique et par thermoluminescence d'aliments ionises". Aix-Marseille 3, 1999. http://www.theses.fr/1999AIX30041.
Abstract (sommario):
L'ionisation est un procede recent qui permet d'assainir et d'augmenter la duree de conservation des aliments. Cette technique est amenee a se developper dans un proche avenir, les autorisations de mise sur le marche de produits ayant subi un traitement ionisant etant en nombre croissant. Afin de pouvoir faire respecter l'etiquetage, il est important de pouvoir mettre en evidence ce type de traitement. Pour cela il existe cinq protocoles officiellement reconnus mais aucun ne s'applique aux coquillages. Ce travail a consiste d'une part a mettre au point de nouveaux protocoles d'identification d'aliments ionises, et d'autre part a permettre la revision de ceux existant deja. Afin de supprimer des problemes d'intoxication dus a la presence de bacteries, il est fort probable qu'un pays comme les etats-unis autorise dans un proche avenir le traitement ionisant des coquillages aussi bien a l'etat frais que congele. Nous nous sommes donc interesses dans un premier temps a la detection par resonance paramagnetique electronique (rpe) et par thermoluminescence (tl) de coquillages ionises. Ces deux techniques physiques bien adaptees pour des produits solides et secs nous ont permis de mettre en evidence trois familles de coquillages irradies presentant chacune un signal different. L'utilisation de techniques telles que l'infrarouge, la diffraction par rayons x ou encore la technique de torche a plasma nous a permis d'expliquer les differences existant entre les divers echantillons temoins ou irradies. La duree du signal etant dans tous les cas detectable bien au dela du temps de stockage, nous avons pu proposer deux protocoles de detection de coquillages ionises, un par rpe et un par tl. Nous nous sommes egalement interesses a la detection d'autres produits comme les fruits, les legumes deshydrates ou encore les epices. En ce qui concerne la detection des fruits par rpe, nous avons pu etablir une classification en fonction du signal observe. Ces signaux sont de trois sortes, type cellulose, type sucre et type amidon. Notre etude a permis d'elargir le champ d'application du protocole de detection par rpe de produits riches en cellulose. Nous avons utilise la tl pour la detection de legumes et de fruits deshydrates. Ce travail a fait l'objet d'une intercomparaison entre plusieurs laboratoires europeens et a conduit a l'elargissement du domaine d'application. Apres avoir applique la methode officielle de detection par tl sur du poivre ionise, nous avons mis au point une methode alternative et propose un protocole. Cette methode alternative permet un gain de temps considerable.
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Florentín, Matthieu. "Irradiation impact on optimized 4H-SiC MOSFETs". Doctoral thesis, Universitat Politècnica de Catalunya, 2016. http://hdl.handle.net/10803/395187.
Abstract (sommario):
Silicon (Si) power device’ technologies have reached a high maturity level, but current
limitations on mechanic, temperature operation and electric performances require to investigate other semiconductor materials that can potentially compete with and overcome those border issues. This is the case of Silicon Carbide (SiC) and Gallium Nitride (GaN) which are becoming serious competitors to the Si due to their superior physical properties. Concerning SiC, the 4Hpolytype seems to be the best suitable candidate for high power MOSFETs according to its band gap, electric field strength, electron bulk mobility, and attainable threshold voltage, among others. But still, technological processes must be optimized in order to SiC MOSFETS can compete with their Si counterparts. This is the case of the gate oxidation process. A reduction of interface charge density is required for threshold voltage stability, and further improvements of the interface quality are also needed for high inversion mobility values. Once solved these problems, a path toward new perspectives of high power applications will be opened.
This work is the direct continuation of the Aurore Constant’s work. It is focused on 4HSiC
based devices, more specifically on the gate oxidation processes and their behaviour under
different harsh environments. Up to now, most of the works carried out were focused on the
improvement of the Silicon Dioxide-Silicon Carbide (SiO2/SiC) interface quality. Solving those
problems would allow designing high-speed and low-switching losses MOSFETs. In the past
work, the main strength was focused on a new surface pre-treatment and on a gate oxidation
process. Results showed improved electrical performances. However, we are convinced that
better values can be obtained by optimizing the post-oxidation annealing step, by performing
surface counter doping or by performing special irradiation treatments. All the efforts of this
work will oriented to the development of reliable SiC MOSFETs with improved electrical
parameters, which can operate under harsh environments (like high temperature or
proton/electron irradiated environment). Thus, the mains guidelines of this Ph. D. Thesis are in accordance with the following lines:
1. State of the art on various SiC related fields.
2. Electrical characterization processes.
3. Proton irradiation impact on 4H-SiC MOSFETs and charge build-up mechanisms theory at
the SiO2/SiC interface.
4. Electron irradiation impact on 4H-SiC MOSFETs.
5. Gate oxidation and implantation processes optimization.
6. Robustness limit of the improved processes under irradiation environments.Las tecnologías de dispositivos de potencia en silicio (Si) han alcanzado una gran madurez. Sin embargo, las limitaciones del Si debidas a sus restricciones mecánicas, térmicas y eléctricas hacen necesario otros materiales semiconductores que puedan competir con el Si y superar sus limitaciones. Este es el caso del Carburo de Silicio (SiC) y del Nitruro de Galio (GaN) que ya comienzan a ser serios competidores del Si debido a sus mejores propiedades físicas. En lo que respecta al SiC, el politipo 4H es el candidato más adecuado para la integración de MOSFETs de potencia debido, entre otros, a los valores del bandgap, campo eléctrico crítico, movilidad volumíca de los electrones y tensión umbral alcanzable. A pesar de estas ventajas teóricas del material, es necesario optimizar cada uno de los procesos tecnológicos involucrados en la fabricación de un MOSFET en SiC para que realmente pueda competir con su contrapartida en Si. Este es el caso del proceso de oxidación para la formación del dieléctrico de puerta. Concretamente, una buena estabilidad de la tensión umbral del componente requiere disminuir la densidad de cargas en la interfase óxido/semiconductor, y mejoras adicionales en la calidad de esta interfase son también necesarias para obtener altos valores de la movilidad de los portadores en el canal de inversión. La solución de los problemas tecnológicos anteriormente enunciados abrirá nuevas perspectivas a las aplicaciones de alta potencia. Este trabajo es una continuación directa del de Aurore Constant. Se centra en dispositivos basados en 4H-SiC, y más específicamente en los procesos de oxidación de puerta, y de sus comportamientos eléctricos en diferente ambientes de trabajo hostiles. Hasta la fecha, la mayor parte de la investigación se ha centrado en la mejora de la calidad de la interfase dióxido de silicio/carburo de silicio (SiO2/SiC). La solución de estos problemas debería permitir el diseño de MOSFETs muy rápidos y con pérdidas de conmutación muy bajas. El objetivo del trabajo previo de Aurore Constant fue encontrar un nuevo procedimiento de limpieza de la superficie antes de realizar la oxidación, y en definir un nuevo proceso de oxidación para la formación del dieléctrico de puerta. Los resultados obtenidos mostraron claras mejoras del comportamiento eléctrico de los componentes. Sin embargo, estamos convencidos que la mejora podría ser aún mayor optimizando la etapa del recocido post-oxidación, utilizando un proceso adicional de dopaje superficial, o realizando un adecuado proceso de irradiación. Todos los esfuerzos de este trabajo se han dirigido al desarrollo de MOSFETs en SiC fiables, con mejores características eléctricas, y capaces de trabajar en ambientes de alta temperatura y de irradiación protónica o electrónica. En resumen, las principales líneas de esta Tesis son las siguientes: 1. Estado del arte de los diferentes dominios de trabajo del SiC. 2. Procesos y técnicas de caracterización eléctrica. 3. Impacto de la irradiación de protones en MOSFETs fabricados en 4H-SiC, y descripción teórica de los mecanismos de creación de carga en la interfase SiO2/SiC. 4. Impacto de la irradiación electrónica en MOSFETs fabricados en 4H-SiC. 5. Optimización de los procesos de oxidación y de implantación. 6. Límite de robustez de los procesos tecnológicos optimizados en ámbitos irradiados.
43
Hayward, Erin M. G. "Atomistic studies on irradiation damage in iron". Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34004.
Abstract (sommario):
Two topics involving irradiation damage in alpha-iron have been considered. First, damage cascades representative of those that would be induced by radiation have been simulated using molecular dynamics (MD). The number and type of defects produced are compared for pure iron and iron with a small hydrogen concentration. Second, the inter- action energy between point defects and line dislocations has been calculated for a number of configurations, using both molecular statics methods and calculations based on linear elastic continuum theory and the dipole force tensor. Results from both methods are com- pared. Results from these two topics are relevant for predicting macroscopic behaviors such as creep and plasticity in reactor structural materials.
44
Canitez, Nazife. "Pasteurization of Apple Cider with UV Irradiation". Fogler Library, University of Maine, 2002. http://www.library.umaine.edu/theses/pdf/CanitezN2002.pdf.
45
Tabtiang, Arunee. "Irradiation crosslinking of oriented plasticised PVC compounds". Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/12433.
Abstract (sommario):
Plasticised polyvinyl chloride (PPVC) compounds were biaxially stretched, annealed in the drawn state and subsequently exposed to electron beam irradiation. During sample irradiation the crosslinking reaction was promoted by a radiation sensitising monomer, trimethylolpropanetrimethacrylate (TMPTMA), included in the PVC compound formulations. The influence of stabiliser type and level, TMPTMA level and irradiation dose on the network structure produced was investigated. A tin stabiliser, Stanclere TL, was selected for this study as it promoted the crosslinking reaction and it showed no interfering peaks in the wide angle x-ray diffraction (WAXD) traces which were used to follow the development of structural order. The appearance of gel, the material insoluble in THF, in irradiated oriented samples proved that a crosslinked structure was created. The gel formation increased with TMPTMA level and irradiation dose. The gel content was found to affect mechanical properties at elevated temperatures and produced an increase in the area shrinkage temperature. Sample thickness and the plasticiser content were found to have a major effect upon gel formation. The thicker the sample was, the smaller the quantity of gel that was formed. Samples containing 46.5phr plasticiser showed greater gel content than samples containing 25phr plasticiser as a result of the higher molecular mobility in the more plasticised samples. It was also found that the orientation of the film decreased the efficiency of network formation in PVC formulations with a 46.5phr plasticiser content but no significant change in gel content could be detected in those containing 25phr plasticiser. Tensile properties and impact strength at room temperature were slightly improved in irradiated samples. The modified structure resulted in an improvement in tensile strength and penetration resistance at higher temperatures and an increased area shrinkage temperature. Crosslinking did not affect room temperature recovery or crystalline orientation; however irradiation crosslinking reduced crystallinity.
46
Franzén, Lars. "Effects of fractionated irradiation on salivary glands". Doctoral thesis, Umeå universitet, Onkologi, 1992. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-101770.
Abstract (sommario):
The thesis is a study of the effects of radiation on the salivary glands in an experimental and a clinical study. Irradiation is a cornerstone in the management of head and neck cancer and is as other modalities of cancer treatment, afflicted with adverse reactions. An optimal radiotherapy regime is limited by the sensitivity of the normal tissues with regard to early and late effects. In certain cases the early effects can be so troublesome that it will cause interruption in the irradiation and questioning of the curative intention. Although DNA is the lethal target, other parts of the cell have been proposed as sensitive targets to irradiation. Different in vitro secretory models and quantitative morphological characterization and immunohistochemical evaluation of neuropeptides were performed in rat salivary glands after irradiation. The irradiation was given unilaterally or bilaterally once a day for a five-day schedule with 6 MV photons (total dose 20, 30, 35, 40, 45 Gy) or a two fractions regime in five days with a total dose of 24 or 32 Gy. The contralateral gland served as a control for unilaterally treated animals and parallel analyses were done 10 days or 180 days following the last irradiation dose. An early, dose-dependent effect of fractionated irradiation on noradrenaline-stimulated potassium fluxes (86Rb+ fluxes) was demonstrated. In contrast, the exocytotic amylase release displayed no obvious alterations, and morphologically no changes were seen. Regarding late effects (180 days) the noradrenaline-stimulated electrolyte secretion was decreased at least for the higher doses of irradiation. Amylase content and loss of acini was also dose-dependently decreased. At 10 days after bilateral irradiation there was a marked increase in the expression of the neuropeptides substance P, leu-enkephalin and bombesin in the ganglionic cells associated with the submandibular glands and in nerve fibers of the glandular parenchyme. In addition, a clinical prospective evaluation of 25 patients was performed before, during radiotherapy and 6, 12 and 18 months after the end of treatment. A great interindividual variation in the recovery was demonstrated with regard to salivary flow rate. Irradiation doses about 40-50 Gy caused generally reversible changes; sometimes salivary secretion was almost completely restored 6-18 months after the end of radiotherapy. Doses exceeding 65 Gy induced almost irreversible alterations. Even if DNA is the target for the lethal effect of irradiation, other constituents, such as the cell membrane or neuropeptide expression can be significantly affected by irradiation and cause important physiological changes.S. 1-43: sammanfattning, s. 47-164: 6 uppsatser
digitalisering@umu
47
El-Shaweesh, Kamal Husein. "Tissue culture and irradiation studies in Solanum". Thesis, University of Salford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334320.
48
Amjad, Muhammad. "Seed irradiation in relation to moisture content". Thesis, University of Salford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281596.
49
Murphy, Susan Mary. "Theory of compositional effects in irradiation damage". Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670365.
50
London, Andrew James. "Irradiation damage of oxide dispersion strengthened steels". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:4860651a-e919-449c-9e1c-8c6843adddd2.
Abstract (sommario):
Advanced fission and fusion power offer long-term energy production from fundamentally carbon-free fuel sources, with high-energy densities and high reliability. However, for these power sources to be realised, many materials challenges need to be addressed. Oxide dispersion strengthened (ODS) ferritic alloys are recognized as potential fission fuel cladding and fusion structural materials because of their high-temperature stability and swelling-resistance imparted by the nano-scale oxide clusters they contain. This work presents the study of a set of model ODS alloys with a systematic variation in alloy chemistry in order to investigate the influence of chemical additions on the oxide cluster nature and the irradiation resistance. To investigate these properties, the high-resolution characterisation techniques of atom probe tomography and transmission electron microscopy were applied in combination with nanoindentation to assess mechanical properties and X-ray diffraction to study the crystallinity. The quantification of the character of the oxide particles in these ODS alloys by atom probe tomography presented a number of challenges and I extend the conventional analysis techniques in order to overcome these difficulties. By comparison of the addition of Ti, and then Cr, to a Fe-Y2O3 alloy, the influence of alloy chemistry on the oxide particles was evaluated. The main aims were to investigate the microstructure, the oxide cluster composition and to set a baseline to which the irradiated samples were compared. The irradiation damage of the oxide clusters was investigated using ion irradiation as an analogue for neutron damage. Irradiation experiments were performed at a range of temperatures and the stability of the clusters was assessed based on their size, number density and chemistry. Subtle changes in cluster chemistry at elevated temperatures and the dramatic changes which occurred after irradiation at low temperatures lead to conclusions about the competition of thermal diffusion and irradiation damage.