Étude du rôle des défauts ponctuels dans la thermoluminescence de monocristaux d'alumine-alpha (effets des traitements thermiques)

Ce travail de recherche concerne les relations qui existent entre la thermoluminescence (TL) et les défauts ponctuels présents dans les monocristaux d'alumine-alpha, en vue d'une application à la dosimétrie des rayonnements ionisants. Les mesures d'absorption optique, fluorescence et 3D-TL nous ont permis de mettre en évidence l'existence de plusieurs centres de piégeage et de recombinaison dans les cristaux et de proposer une corrélation entre la nature électron/trou des pièges et le mécanisme de recombinaison correspondant. (...) L'approfondissement et la caractérisation des effets interactifs entre les divers pièges nous ont permis d'expliquer la variation de la sensibilité du pic dosimétrique lors des cycles de mesures consécutifs, l'extinction thermique de la thermoluminescence du pic dosimétrique et la variation de la sensibilité des divers pics de TL en fonction de la température d'irradiation. Nous avons utilisé (...) la technique d'annihilation des positrons, complétée par des mesures RPE, pour suivre la concentration de lacunes d'aluminium en fonction de l'atmosphère des traitements thermiques. (...). La dernière partie de l'étude est focalisée sur le rôle des impuretés telles que le titane, le fer et le chrome. (...)NICE-BU Sciences (060882101) / SudocST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceHungaryFRH

Determination of furanic compounds in insulating oil by high performance liquid chromatography mass spectrometry using atmospheric pressure chemical ionization

A method has been developed to determine furanic compounds in insulating oil matrix using liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization. The examined samples were provided from model experiments and also from several high voltage functioning transformers. To increase sensitivity of the method six furanic compounds (determined by model experiments) were quantified by selected ion monitoring, and quantitation was based on the marker peaks. Oil samples were prepared using solid phase extraction. The results are suitable for evaluation of model experiments and also to solve problems of calibration. From extracts of oil samples taken from functioning transformers cellulose depolymerization products have been identified, and their amounts were found to be valuable in assessing the condition of the transformer (fault diagnosis

Thermally Stimulated Luminescence and Exoelectron Emission Mechanism of the 430 K (D') Dosimetric Peak of alpha-Al2O3

International audienceSeveral alpha-Al2O3 samples were studied in order to determine the mechanism of electron-hole processes of the 430 K (D') thermoluminescence (TL) and thermally stimulated exoelectron emission (TSEE) dosimetric peak. Single crystals prepared in highly reducing conditions were treated in different atmospheres (reducing/oxidizing) and their optical absorption (after isochronous annealing), fluorescence and TL properties were investigated. From these results an electron trap is suggested for the 430 K peak which is in contradiction to some data taken from the literature: this problem is then discussed. Pure and Th4+ doped alpha-Al2O3 powders were studied by TL methods regarding doping concentration and preparation conditions. In this way the role of aluminum vacancies is proved. Considering these new results, literature data and different hypotheses, the possible nature of the trap is discussed