Dissertations / Theses on the topic 'Thermoluminescence'

The kinetic and dosimetric features of the main thermoluminescence peak of quartz have been investigated in unannealed as well in quartz annealed at 500˚C for 10 minutes. The main peak is found at 92 and 86˚C respectively for aliquots of unannealed and annealed samples irradiated to 10 Gy and heated at 5.0˚C/s. For each sample, the intensity of the main peak is enhanced with repetitive measurement whereas its maximum temperature is unaffected. The peak position of the main peak in each sample is independent of the irradiation dose and this, together with its fading characteristics are consistent with first-order kinetics. For low doses, typically between 2 and 10 Gy, the dose response of the main peak in each sample is linear. In the intermediate dose range from 10 to 60 Gy, the growth of the main peak in each sample is sub-linear and for greater doses, in the range from 60 Gy to 151 Gy, it is linear again. The half-life of the main peak of the unannealed sample is about 1.3 h whereas that of the annealed sample is about 1.2 h. The main peak in each sample can be approximated to a first-order glow peak. As the heating rate increases, the intensity of the main peak in each sample decreases. This is evidence of thermal quenching. The main peak in each sample is the only peak regenerated by phototransfer. The resulting phototransferred peak occurs at the same temperature as the original peak and has similar kinetic and dosimetric features. For a preheat temperature of 120˚C, the intensity of the phototransferred peak in each sample increases with illumination time up to a maximum and decreases afterwards. At longer illumination times (such as 30 min up to 1 h), no further decrease in the intensity of the phototransferred peak is observed. The traps associated with the 325˚C peak are the main source of the electrons responsible for the regenerated peak. Radioluminescence emission spectra were also measured for quartz annealed at various temperatures. Emission bands in quartz are affected by annealing and irradiation. A strong enhancement of the 3.4 eV (~366 nm) emission band is observed in quartz annealed at 500˚C. A new emission band which grows with annealing up to 1000˚C is observed at 3.7 eV (~330 nm) for quartz annealed at 600˚C. An attempt has been made to correlate the changes in radioluminescence emission spectra due to annealing with the influence of annealing on luminescence lifetimes in quartz.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Quartz is one of the most abundant natural minerals in the crust of the earth. Due to its dosimetric luminescence properties, it is employed in retrospective dosimetry, archaeological and geological dating. The intensity and the structure of the TL glow curves of quartz are strongly dependent upon the origin, impurity content, formation condition and pre-irradiation heat treatment. The aim of this project is to study the mechanisms of thermoluminescence (TL), Phototranssferred thermoluminescence (PTTL) and radioluminescence (RL) in synthetic quartz and to discuss the results in terms of physical characteristics of point defects involved. Thermoluminescence measurements were made on a sample of synthetic quartz in its as-received state (unannealed) synthetic quartz annealed at 500˚C for 10 minutes. The unannealed sample shows six TL glow peaks located at 94, 116, 176, 212, 280 and 348˚C at a heating rate of 5˚Cs⁻¹. The annealed sample shows seven TL peaks at 115, 148, 214, 246, 300, 348 and 412˚C at a heating rate of 5˚Cs⁻¹. The intensity of peak I, at 94 and 115˚C for the unannealed and annealed samples respectively, increases with irradiation. Peak I has an activation energy of approximately 0.90 eV and a frequency factor of the order of 10¹¹ s⁻¹. The order of kinetics is between 0.9 and 1.2. The unannealed synthetic quartz shows phototransferred thermoluminescence (PTTL) at the position of peak I after removal of the first three peaks followed by illumination. The PTTL intensities show peak shaped behaviour when plotted against illumination time. The PTTL showed a quadratic increase with dose. The material exhibits fading of PTTL intensity with delay time. Radioluminescence was measured on synthetic quartz unannealed and annealed annealed at 500, 600, 700, 800, 900 and 1000˚C for 10 to 60 min. The emission spectra of synthetic quartz show seven emission bands. The effect of irradiation on the RL spectra is to increase the intensity of all emission bands for samples annealed at temperatures less than or equal to 700˚C. The effect of annealing time is to increase the RL amplitude for the samples annealed at temperatures greater than 700˚C. The annealing temperature increases the RL amplitude of all emission bands of the spectrum for all samples.

The kinetic and dosimetric features of the main thermoluminescent peak of synthetic quartz have been investigated in quartz ordinarily annealed at 500_C as well as quartz annealed at 500_C for 10 minutes. The main peak is found at 78 _C for the samples annealed at 500_C for 10 minutes irradiated to 10 Gy and heated at 1.0 _C/s. For the samples ordinarily annealed at 500_C the main peak is found at 106 _C after the sample has been irradiated to 30 Gy and heated at 5.0 _C/s. In these samples, the intensity of the main peak is enhanced with repetitive measurement whereas its maximum temperature is unaffected. The peak position of the main peak in the sample is independent of the irradiation dose and this, together with its fading characteristics, are consistent with first-order kinetics. For doses between 5 and 25 Gy, the dose response of the main peak of the annealed sample is superlinear. The half-life of the main TL peak of the annealed sample is about 1 h. The activation energy E of the main peak is around 0.90 eV. For a heating rate of 0.4 _C/s, its order of kinetics b derived from the whole curve method of analysis is 1.0. Following irradiation, preheating and illumination with 470 nm blue light, the main peak in the annealed sample is regenerated during heating. The resulting phototransferred peak occurs at the same temperature as the original peak and has similar kinetic and dosimetric features, with a half-life of about 1 h. For a preheat temperature of 200 _C, the intensity of the phototransferred peak in the sample increases with illumination time up to a maximum and decreases thereafter. At longer illumination times, no further decrease in the intensity of the phototransferred peak is observed. The traps associated with the 325 _C peak are the main source of the electrons responsible for the regenerated peak.

In this work, initially the radioluminescence (RL) and thermoluminescence (TL) techniques are presented. The radioluminescence is the prompt luminescence emitted by a material under ionizing radiation exposure. The thermoluminescence is the luminescence emitted by a material previously exposed to ionizing radiation when excited by heat. Enegy bands concepts, defects in crystals and the different processes of ionization that take place in matter when exposed to ionizing radiation are briefly discussed in order to present the mechanisms involved in RL and TL processes. The usage of the techniques in characterization of materials and dosimetry is reported, legitimating the importance of the instrument developed. Mechanical and structural parts as well as a description of each component of the instrument are fairly described. The implemented algorithm for controlling the instrument and acquiring data is also discussed. The development of the instrument enabled us to generate temperature ramps with a quite good performance, reaching temperatures up to 500 °C with deviations up to 2 °C, having used heating rates between 0.5 °C/s and 5 °C/s. Calibrations of optical spectrometer used in light collection and irradiation system were carried out. Lastly, TL and RL spectra tests were performed. The RL tests were carried out using several materials which emission spectra are well known by literature, namely, carbon-doped aluminium oxide Al2O3:C, terbium-doped gadolinium oxysulphide Gd2O2S:Tb, europium-doped yttrium oxide Y2O3:Eu and dysprosium-doped calcium borate CaB6O10:Dy. For the TL spectra test, the aluminium oxide doped with carbon Al2O3:C was used. The results of RL and TL spectra tests showed a good agreement with the literature, pointing out that the instrument developed in this work is comparable to others instruments in operation from others research groups, making our results reliable.
Nesse trabalho, inicialmente as técnicas de radioluminescência (RL) e termolumi- nescência (TL) são apresentadas. A radioluminescência é a luminescência imediata emitida por um material quando exposto à radiaçao ionizante. A termoluminescência é a luminescência emitida por um material previamente exposto à radiação quando este é aquecido. Conceitos de bandas de energia, defeitos em cristais e os diferentes processos de ionização que ocorrem na matéria quando exposta à radiação ionizante são brevemente discutidos a fim de apresentar os mecanismos envolvidos na RL e TL. A utilização das técnicas na caracterização de materiais e na dosimetria é reportada, justificando a importância do instrumento desenvolvido. As partes mecânicas/estruturais e uma descrição de cada componente do instrumento são descritos. O algoritmo implementado para controle do instrumento e aquisição de dados é também descrito. O desenvolvimento do instrumento possibilitou a geração de rampas de temperatura com uma boa performance, atingindo até 500 °C com variações de até 2 °C ao utilizar taxas de aquecimento entre 0.5 °C/s e 5 °C/s. Calibrações do espectrômetro óptico utilizado na aquisição da luminescência e do sistema de irradiação foram executadas. Por fim, testes de aquisição de espectros de RL e TL foram realizados. Os testes de RL foram realizados utilizando vários materiais cujos espectros de emissão são bem conhecidos pela literatura, a saber, óxido de alumínio dopado com carbono Al2O3:C , oxisulfeto de gadolínio dopado com térbio Gd2O2S:Tb , óxido de ítrio dopado com európio Y2O3:Eu e borato de cálcio dopado com disprósio CaB6O10:Dy. Para o teste dos espectros de TL, o Al2O3:C foi utilizado. Os resultados dos espectros de RL e TL mostraram concordância com a literatura, indicando que o instrumento desenvolvido é comparável a outros instrumentos em operação de outros grupos, tornando os nossos resultados confiáveis.

Tous les feldspaths ne peuvent etre dates par la methode de la thermoluminescence. En effet un certain nombre presente une perte anormale du signal de thermoluminescence naturelle. Pour comprendre l'origine de cette perte, nous avons travaille sur une quarantaine de feldspaths de divers origines. Les etudes ont porte sur la mesure de la thermoluminescence et de l'effet tunnel, sur l'emission en cathodoluminescence, radioluminescence x et en photoluminescence, sur l'excitation. Nous avons etudie le comportement au stockage, ainsi qu'au blanchiment optique de la thermoluminescence. Les conclusions de cette etude sont les suivantes: - la perte anormale de la tl dans les feldspaths est du a l'effet tunnel. La mesure de l'effet tunnel donne une idee juste de l'importance de cet effacement. - les microclines sont peu affectees par l'effet tunnel, et peuvent par consequence etre utilisees en datation tl. - pour les sanidines, la perte anormale interdit toute datation dans la bande spectrale bleue (250 nm- 590 nm). Mais on peut esperer pouvoir les dater en se servant de l'emission tl infrarouge, centree sur 700 nm et attribuee a fe3+. Ce resultat est interessant pour la datation de laves volcaniques

In the various brachytherapy techniques the intent is to deliver as high a tumour dose as possible, limited only by surrounding normal tissue tolerance. The main feature of the techniques is very steep dose gradients, representing a potential limiting factor in accurate dose distribution measurements around sources. Dose distributions at distances less than 1 cm are therefore normally generated using either validated Monte Carlo (MC) simulations or standard dose calculation formalisms, for example that of AAPM TG 43, while dose measurements can only be performed at larger distances, normally greater than 1 cm from the outer dimensions of the source encapsulation Ge-doped silica fibres are a viable thermoluminescent dosimetry (TLD) system, providing good spatial resolution of approximately 120 urn, sensitive response to ionizing radiations, large dynamic dose range, good reproducibility and reusability, dose rate independence, minimal fading, resistance to water and low cost. Dosimetric characterisation of commercial Ge-doped silica fibres have been obtained by subjecting them to kilovoltage therapeutic x-ray radiation beams, verifying their use for brachytherapy sources; dose response, reproducibility and fading at 90 kVp and 300 kVp have been investigated. Central-axis depth doses have been obtained at the two accelerating potentials using different field size applicators, measurements being made using the fibres in both water and a GAMMEX RMr 4571 solid water phantom. Comparison has been made with central-axis depth doses, measured using a 0.6 cm3 graphite-walled ionisation chamber data and British Journal of Radiology Supplement 25 tabulated values (both in water). Ge-doped optical fibre dosimeters show good dosimetric response for low photon energies. These desirable characteristics support the use of these TL fibres as dosimeters for brachytherapy applications. Ge-doped optical fibre TL dosimeters have been used to measure the dose distribution around two Low Dose Rate (LDR) 125r seeds; model 6711, the new thinner model 9011 and a High Dose Rate (HDR) 192rr (MicroSelectron V2) source at proximal distances down to 1 mm, measured in a Perspex medium. The anisotropy has also been measured in Perspex, for distances from 10 to 100 mm from a LDR 1251 seed model 6711 centre, in 10 mm increments and at angles 10° to 90° in 10° increments from the seed central axis. Measured doses have been compared with calculations and treatment planning system (TPS) predicted doses for the same locations. Monte Carlo simulations were obtained using the EGSnrc \ DOSRZnrc codes and TPS predicted doses were obtained using the system VariSeed V8.0.2. For 1251 seed model 6711, the measurements agree with simulations to within 2.3 % ± 0.3 % along the transverse and perpendicular axes and within 3.0 % ± 0.5 % for measurements investigating anisotropy in angular dose distribution. Measured and Veriseed™ brachytherapy treatment planning system (TPS) values agreed to within 2.7 % ± 0.5 %. For the new thinner 1251 model 9011, dose measurements were in good agreement with simulations to within 2.1 ± 0.2 %, while dose measurements and doses obtained through use of the Variseed TPS agreed well, to within 2.2 ± 0.5 %. The above work has therefore demonstrated the applicability of Ge-doped optical fibres for use in brachytherapy.

Carbon-doped aluminium oxide, α-Al₂O₃ : C, is a highly sensitive luminescence dosimeter. The high sensitivity of α-Al₂O₃ : C has been attributed to large concentrations of oxygen vacancies, F and F⁺ centres, induced in the material during its preparation. The material is prepared in a highly reducing atmosphere in the presence of carbon. In the luminescence process, electrons are trapped in F-centre defects as a result of irradiation of the material. Thermal or optical release of trapped electrons leads to emission of light, thermoluminescence (TL) or optically stimulated light (OSL) respectively. The thermoluminescence technique is used to study point defects involved in luminescence of α-Al₂O₃ : C. A glow curve of α-Al₂O₃ : C, generally, shows three peaks; the main dosimetric peak of high intensity (peak II) and two other peaks of lower intensity called secondary glow peaks (peaks I and III). The overall aim of our work was to study the TL mechanisms responsible for secondary glow peaks in α-Al₂O₃ : C. The dynamics of charge movement between centres during the TL process was studied. The phototransferred thermoluminescence (PTTL) from secondary glow peaks was also studied. The kinetic analysis of TL from secondary peaks has shown that the activation energy of peak I is 0.7 eV and that of peak III, 1.2 eV. The frequency factor, the frequency at which an electron attempts to escape a trap, was found near the range of the Debye vibration frequency. Values of the activation energy are consistent within a variety of methods used. The two peaks follow first order kinetics as confirmed by the TM-Tstop method. A linear dependence of TL from peak I on dose is observed at various doses from 0.5 to 2.5 Gy. The peak position for peak I was also independent on dose, further confirmation that peak I is of first order kinetics. Peak I suffers from thermal fading with storage with a half-life of about 120 s. The dependence of TL intensity for peak I increased as a function of heating rate from 0.2 to 6ºCs⁻¹. In contrast to the TL intensity for peak I, the intensity of TL for peak III decreases with an increase of heating rate from 0.2 to 6ºCs⁻¹. This is evidence of thermal quenching for peak III. Parameters W = 1.48 ± 0:10 eV and C = 4 x 10¹³ of thermal quenching were calculated from peak III intensities at different heating rates. Thermal cleaning of peak III and the glow curve deconvolution methods confirmed that the main peak is actually overlapped by a small peak (labeled peak IIA). The kinetic analysis of peak IIA showed that it is of first order kinetics and that its activation energy is 1:0 eV. In addition, the peak IIA is affected by thermal quenching. Another secondary peak appears at 422ºC (peak IV). However, the kinetic analysis of TL from peak IV was not studied because its intensity is not well defined. A heating rate of 0.4ºCs⁻¹ was used after a dose of 3 Gy in kinetic analysis of peaks IIA and III. The study of the PTTL showed that peaks I and II were regenerated under PTTL but peak III was not. Various effects of the PTTL for peaks I and II for different preheating temperatures in different samples were observed. The effect of annealing at 900ºC for 15 minutes between measurements following each illumination time was studied. The effect of dose on secondary peaks was also studied in this work. The kinetic analysis of the PTTL intensity for peak I showed that its activation energy is 0.7 eV, consistent with the activation energy of the normal TL for peak I. The PTTL intensity from peak I fades rapidly with storage compared with the thermal fading from peak I of the normal TL. The PTTL intensity for peak I decreases as a function of heating rate. This decrease was attributed to thermal quenching. Thermal quenching was not observed in the case of the normal TL intensity. The cause of this contrast requires further study.

Le sujet de ce travail est l'étude du Paléogène marin de la zone alpine externe. Son objet : rechercher par l'analyse détaillée des unités lithostratigraphiques externe. Son objet : rechercher par l'analyse détaillée des unités lithostratigraphiques formelles, des données et des schémas paléogéographiques cohérents qui permettent de préciser l'évolution tectono-sédimentaire de la marge interne de la plaque européenne au cours de la période paléogène. La principale méthode d'investigation utilisée est la thermoluminescence (TL), en association avec des méthodes d'étude plus classiques empruntant à la biostratigraphie, à la pétrographie et à l'analyse structurale. Quatre parties constituent le présent mémoire. La première partie est d'ordre méthodologique. Successivement , sont précisés: la phénoménologie de la thermoluminescence, les modalités d application de la méthode d'analyse dans le domaine des Sciences de la Terre, les différentes techniques expérimentales utilisées, le choix des paramètres TL et leur traitement statistique. La seconde partie traite des relations entre la thermoluminescence et le métamorphisme mésoalpin. Ce métamorphisme, qui affecte irrégulièrement les matériaux paléogènes et leur substratum, est générateur d'une thermoluminescence de néogenèse dont les caractères spécifiques sont appréhendés grâce à l'analyse des filons de quartz syn- à tardimétamorphes post-priaboniens. Les effets de ce métamorphIsme sont variables et sélectifs à l'échelle des Alpes occidentales,limités dans la zone alpine externe, plus importants dans le domaine interne - notamment dans le Briançonnais - où ils peuvent entraîner l'effacement partiel ou total des caractères thermoluminescents originels du quartz et introduire une part d'incertitude non négligeable dans le raisonnement et les conclusions d'ordre paléogéographique. La troisième partie est consacrée à l'étude régionale des formations détritiques paléogènes de la zone alpine externe affleurant dans les Alpes maritimes s .l., dans le Champsaur et dans le Dévoluy, dans le Pays des Arves et en Haute-Savoie. L'emploi de diagrammes bidimensionnels et de cartes isofactes prenant en compte les paramètres de thermoluminescence les plus performants permet de défInir les principales provinces distributives de matériaux terrigènes, de faire la part des apports d'origine externe et interne lors des différents stades de remplissage des bassins et sous-bassins paléogènes dont l'évolution paléogéographique et structurale est également précisée par l'établissement de cartes de paléofaciès et par l'analyse de la déformation des matériaux à toutes les échelles. Le modèle géodynamique proposé en conclusion, dans la dernière partie du mémoire, lie intimement la sédimentation et la déformation progressive des flyschs crétacés allochtones et des flyschs paléogènes d'avant-pays dans les Alpes occidentales. Il considère l'ensemble de ces flyschs comme un continuum de formations synorogéniques déposées dans des bassins convergents installés par subsidence "forcée' à l'avant de chevauchements crustaux actifs engendrés par la collision Europe-Afrique à partir de l'Albien terminal, le remplissage des bassins sédimentaires étant d'abord assuré par des reliefs bordiers externes rajeunis par le développement de bombements lithosphériques, puis par les parties internes de l'orogène intégrant progressivement ces mêmes flyschs dans leurs superstructures.

Ce travail est une contribution a une meilleure comprehension des mecanismes a l'origine de la thermoluminescence des solides inorganiques a l'etat cristallin, en particulier le sulfate de calcium dope aux ions lanthanides ou au manganese, puissant dosimetre utilise notamment en datation par thermoluminescence et l'oxyde mixte de bismuth et de germanium, dont les applications industrielles sont nombreuses, notamment en holographie. Un dispositif de luminescence a tres basses temperatures, a partir de 10k (263#oc) a ete realise. Il permet une analyse spectrale fine des emissions. En ce qui concerne le sulfate de calcium, la nature des centres pieges associes aux pics dans le domaine des basses temperatures a ete proposee. Apres avoir montre l'insuffisance des relations habituelles reliant l'energie d'activation a la seule mesure de la temperature du maximum d'un pic, la mise en evidence d'une composante basse temperature dans le domaine de l'initial rise a permis de proposer un autre mode de traitement des courbes et de caracteriser la profondeur d'un piege par une seule valeur de l'energie d'activation. Nous avons montre que les ions lanthanides et manganese sont excites par un transfert d'energie non radiatif non resonnant. Grace a la resonance paramagnetique electronique, la presence systematique de deux impuretes presentes a l'etat de traces, a ete decelee dans tous les cristaux et la concentration relative impurete/dopant a permis de prevoir l'influence des constituants sur les mecanismes de luminescence. En ce qui concerne l'oxyde mixte de bismuth et de germanium, ce travail a permis d'identifier les niveaux electroniques responsables de ses proprietes opto-electroniques. Nous avons montre que le processus de thermoluminescence est caracterise par un ordre evoluant avec le degre de vidage d'un centre piege. Nous avons egalement montre que la thermoluminescence obeit a une loi expone

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Étude du néolithique marocain. Présentation des procédures de datation par thermoluminescence et des méthodes de dosimétrie TL. Établissement de la chronologie absolue du néolithique marocain entre 3000 et 7000 ans B. P.

Desenvolveu-se um sistema termoluminescente especial, para operar a partir da temperatura do nitrogênio líquido, que permite, ainda, a obtenção do espectro de emissão termoluminescente da amostra. Com o uso deste sistema, estudou-se a termoluminescência do LiF:Mg,Ti (TLD-100), irradiado a 77 K, desde a temperatura de irradiação até 315K. Neste intervalo de temperaturas foram determinados sete picos de emissão termoluminescente em 139, 153, 194, 240, 260, 283 e 300K. Através de experiências de variação do tratamento térmico da amostra, linearidade, fototransferência e destruição óptica, o pico de emissão termoluminescente em 139K foi associado a centros de buracos Vk, enquanto que os demais a armadilhas de elétrons. Os sete picos de emissão termoluminescente emitem em três comprimentos de onda, 270, 300 e 420nm, sendo que a banda de emissão em 270nm é a mais intensa no caso dos picos de emissão termoluminescente em 139 e 153K, sobressaindo-se as bandas de emissão em 300 e 420nm para os demais picos de emissão termoluminescente. A banda de emissão em 270nm foi associada a centros de recombinação para buracos liberados dos centros Vk, centros estes diferentes daqueles, normalmente, associados à banda de emissão em 420nm. Quanto à banda de emissão em 300nm, esta foi associada à interação entre elétrons e centros Vk. Verificou-se que os picos de emissão termoluminescente em 139, 153, 194 e 260K obedecem à cinética de primeira ordem. As energias de ativação determinadas para estes picos foram, respectivamente, 0,26, 0,29, 0,49 e 0,82eV.
A special thermoluminescent system was deve1oped. It is able to operate right from liquid nitrogen temperature and also permits the determination of the sample thermoluminescent emission spectrum. Using this system, the thermoluminescence displayed by 77K irradiated LiF:Mg,Ti (TLD-100), from the irradiation temperature to 315 K, was studied. In this temperature range seven glow peaks, at 139, 153, 194, 240, 260, 283 and 300 K, were determined. Based upon different annealing procedures, linearity, phototransference and optical bleaching experiments, the glow peak at 139 K was related to Vk hole centres, while the remaining glow peaks were associated to electron traps. The seven glow peaks emit at three wavelengths, namely, 270, 300 and 420 nm. The emission band at 270 nm is the most intense in the case of glow peaks at 139 and 153 K. For the remaining glow peaks, the emission bands at 300 and 420 nm are the most important ones. The emission band at 270 nm was related to the recombination of Vk holes at recombination centres other than those ones, normally, associated to the emission band at 420 nm. The emission band at 300 nm was related to the recombination of electrons and Vk centres. It was verified that the glow peaks at 139, 153, 194 and 260 K obey the first order kinetics. For these glow peaks, the determined activation energies were, respectively, 0,26, 0,29, 0,49 and 0,82 eV.

L'originalité de ce travail réside dans le développement de modèles prenant en compte la simultanéité de la Thermoluminescence (TL), de l'Emission Exoélectronique Thermostimulée (EETS) et de la Conductivité Electrique Thermostimulée (CETS) présentées par l'alumine alpha monocristallin. Les modèles sont fondés sur un formalisme qui permet de s'affranchir des hypothèses et approximations rencontrées dans la littérature. Ils tiennent compte du mécanisme thermoi͏̈onique pour l'EETS (1), de l'extinction thermique de la luminescence (2), de la superposition des pics d'EETS (3), de deux approches différentes concernant la condition de neutralité (4) et du gradient thermique dans l'échantillon (5). Ce dernier est à l'origine du caractère multicouche de nos modèles qui permet en outre de distinguer les phénomènes de volume (TL et CETS) des phénomènes de surface (EETS). La validation des modèles est obtenue en comparant les courbes expérimentales de l'alumine aux courbes simulées. L'étude qui a porté principalement sur le pic B' (265 K) et sur le pic dosimétrique D' (450 K) permet de déterminer les paramètres de piégeage liés aux défauts impliqués. Des simulations de l'effet de la vitesse de chauffage puis du rôle de la dose d'irradiation sur la réponse des phénomènes thermostimulés, sont reportées. La corrélation entre la théorie et l'expérience est très satisfaisante
The originality of this work arises from the fact that we have developed new models taking into account simultaneously Thermally Stimulated Luminescence (TL), Thermally Stimulated Exoelectronic Emission (TSEE) and Thermally Stimulated Conductivity (TSC) of alpha-alumina single crystals. The models are based on a formalism allowing to overcome the hypothesis and assumptions published in the literature. In particular, they take into account the thermionic model describing the TSEE process (1), the thermal quenching of luminescence (2), the superimposing of TSEE curves (3), two different approaches concerning the electrical neutrality condition (4) and the thermal gradient in the sample (5). This latter characteristic does explain the multilayer character of the models leading to distinguish between the volume phenomena (TL and TSC) and the surface ones (TSEE). The validation of the models is obtained by comparing the experimental curves with the simulated ones. The study which concerns especially the peak B' (265 K) and the dosimetric one, D' (450 K) allows to evaluate their trapping parameters involved in the related defects. Moreover, simulations based on the role of the heating rate and that of irradiation dose in thermally stimulated phenomena, are reported. The correlation between theory and experiments is quite satisfying

La datation par thermoluminescence (tl) s'applique generalement a des mineraux chauffes et peut donc etre utilisee pour etablir une chronologie absolue des retombees volcaniques (tephra). Elle a ete peu employee jusqu'a present et semblait limitee a des ages inferieurs a 150000 ans. L'extension de la methode pour des ages superieurs a ete possible grace a l'utilisation, pour la premiere fois en datation, du pic tl rouge a 370c du quartz. Son comportement est explique de facon coherente par une theorie specialement developpee et basee sur l'existence de correlations spatiales electron-trou. Vu l'importance de la dosimetrie, un chapitre lui a ete consacre. Les principaux developpements concernent le comptage alpha a scintillation et la prise en compte de l'influence de l'humidite sur la dose annuelle. Les echantillons de tephra dates sont pour la plupart issus de la chaine des puys (massif central, france) mais certains ont ete preleves dans les monts dores ou le velay (massif central, france) et aussi en italie. Les datations proposees avec le pic rouge s'echelonnent de 10000 a 800000 ans avant nous, soit une tres grande latitude chronologique que ne recouvre entierement aucune autre methode de datation sur les tephra. Les principales difficultes sont liees a l'extrapolation des courbes de croissance. Elles pourraient etre levees par l'emploi d'extrapolations plus complexes que celles utilisees dans ce travail et qui s'appuieraient sur le modele theorique decrit dans le memoire

Magnesium tetraborate is a candidate phosphor for a laser-heated thermoluminescence (TL) dosimetry system which is under development. Near tissue-equivalent radiation absorption properties and reported sensitivity to low radiation doses offer advantages over commonly employed LiF phosphors. Sintered wafers suitable for routine measurement were prepared. The effects of powder preparation conditions and activator concentration on TL sensitivity were investigated. Samples with additional impurities (co-doped samples) were prepared in order to increase sensitivity through coactivation or sensitization effects. TL emission spectra were employed to evaluate the effects of co-doping.
Master of Science
incomplete_metadata

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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Tese (Doutoramento)
IPEN/T
Instituto de Fisica, Universidade de Sao Paulo - IF/USP

Ce memoire concerne la determination des debits de dose d'irradiation naturelle dont la connaissance est necessaire dans le cadre de la datation par thermoluminescence (tl). Ils sont faibles et lies a des types d'irradiation varies: particules alpha et beta, rayonnements gamma et cosmiques. Pour une evaluation precise des doses, nous avons d'abord mene un etalonnage des sources de reference utilisees, puis une etude approfondie de la technique de comptage alpha par scintillation. Cette methode de mesure a ete amelioree et etalonnee avec des echantillons de composition bien connue. Les sources d'erreur ont ete etudiees en detail: surcomptage et fuites de radon. Les coefficients d'absorption de la dose beta (utilises dans la methode des inclusions de quartz) deja evalues par mejdhal ont ete repris a partir d'une autre methode avec une tentative de verification experimentale. Dans le but d'ameliorer la mesure de la dose gamma, des methodes analytiques et directes ont ete utilsees: analyses physico-chimiques, gammametrie de site, dosimetrie tl. Ceci a comporte la mise en uvre d'un nouveau dosimetre thermoluminescent, l'alumine activee au carbone et le calcul precis des corrections a apporter a l'etalonnage d'un gammametre. Des mesures faites sur des sites de reference ont permis une comparaison critique des diverses techniques de dosimetrie mises en uvre dans ce travail. La technique de la dosimetrie integree qui consiste a melanger l'echantillon reduit en poudre avec le dosimetre tl a ete testee sur l'alumine insensibilisee aux particules alpha. Cette simulation a permis de mesurer la dose annuelle sans calcul de facteur correctif. Un accord tres satisfaisant s'est degage entre des techniques pourtant totalement independantes

Étude de la dosimétrie des rayonnements d'origine naturelle dans laquelle duex composantes peuvent être distinguées. Dose interne apportée par les rayonnements de faible parcours issus de l'échantillon considéré. Dose externe apportée par les rayonnements de grand pouvoir de pénétration et provenent de l'environnement de l'échantillon. Deux techniques sont traitées en détail: Dosimétrie thermoluminescents et spectrométrie gamma de terrain. Corrections liées à l'environnement et aux conditions d'emploi

Thermoluminescence of synthetic quartz annealed at 1000 ºC for 10 minutes has been studied. The aim was to study mechanisms of thermoluminescence in annealed synthetic quartz and to discuss the results in terms of the physics of point defects. The sample was irradiated with a beta dose of 10 Gy of beta radiation and then heated at a linear heating rate of 1 ºC.s-1 up to 500 ºC. The thermoluminescence (TL) glow curve consists of three glow peaks. Peak I at 74 0C (main peak) with high intensity as compared to the other two peaks. Peak II at 144 ºC is more intense than peak III at 180 ºC. This study was on the main peak (MP) at 74 ºC and peak III at 180 ºC. Kinetic analysis was carried out to determine the trap depth E, frequency factor s and the order of kinetics b of both peaks using the initial rise, peak shape, variable heating rate, glow curve deconvolution and isothermal TL methods. The values of kinetic parameters obtained were around 0.7 to 1.0 eV for trap depth and in the interval of 108 to 1015 s-¹ for frequency factor for both peaks. The effect of heating rate from 0.5 to 5 ºC.s-¹ on the TL peak intensity and peak temperature was observed. Also the effect of thermal quenching was observed at high heating rates. Since the TL glow curve has overlapping TL peaks, the Tm-Tstop method from 54 ºC up to 64 ºC and E -Tstop methods were introduced where a first order single peak was observed. Phototransfered thermoluminescence (PTTL) was investigated and characterized by three peaks. First PTTL peak I at 72 ºC, peak II at 134 ºC and peak III at 176 ºC. Analysis was carried out on peaks I and III for the effect of dose dependence from 20-200 Gy. Thermal fading was observed on PTTL peaks I and III, after storage time of 30 minutes.

The work presented in this thesis details the design, construction, and calibration of a high-sensitivity multispectral thermoluminescence (TL) imaging system, with applications in geophotonics and luminescence dating. The system delivered enhanced spatially-resolved detection capabilities and sufficient sensitivity to accurately quantify the faint spectral emissions from single grains of quartz across multiple detection bands. Such measurement was previously unavailable using current techniques; with existing instrument architecture lacking the targeted detection, required sensitivity, and wavelength resolution made possible by the spatially-resolved imaging of thermoluminescence emissions. The advances presented herein provide i) a viable means of obtaining trapped-charge dose measurements from samples with luminescence emission characteristics for which current techniques are unsuited, and ii) a valuable research tool for investigating the temperature- and wavelength-resolved kinetic processes of thermoluminescence production and the mechanisms which govern these interactions. A design science research approach was adopted; requiring a comprehensive synthesis and understanding of the key elements underpinning instrument development and imaging techniques in luminescence dating applications. These elements included 1) luminescence production mechanisms and models, 2) the kinetic parameters of quartz governing these processes, 3) the current techniques in luminescence dating and existing instrument architecture used to detect and quantify the thermally and optically stimulated luminescence emissions of quartz, and 4) the application of advanced optical imaging systems and techniques to these areas. A comprehensive and systematic evaluation of the instrumentation used in luminescence dating was first undertaken, with a primary focus on the devices used for light collection and the spectral separation of luminescence emissions. These findings, along with fundamental considerations in optical imaging techniques, were used to inform the design and construction of the multispectral thermoluminescence imaging system. The key operational objectives relating to system performance were all met or exceeded, including specifications for quantum efficiency, optical throughput, spectral response, noise performance and sensitivity, as well as unit price and system integration cost. The resultant system delivered enhanced spatially-resolved multispectral detection capabilities previously unavailable using current techniques and existing instrument architecture. The system was developed around a Santa Barbara Instrument Group (SBIG) STT-8300M charge-coupled device (CCD) camera utilizing a Kodak KAF-8300 sensor, with peak quantum efficiency of 56% at approximately 550 nm. The sensor was thermo-electrically cooled to -20 oC during measurement to reduce thermal readout noise, producing dark current threshold values of 0.02e-/pixel/sec. A high-throughput custom-built lens configuration was designed for light collection and imaging, with lenses constructed from uncoated fused silica providing strong transmission (≥95%) across the visible spectrum and deep ultraviolet (UV). An Astrodon Sloan SDSS filter set was chosen for spectral separation of TL emissions, providing five discrete narrow bands of detection with extremely high peak transmission (≥95%), steep wavelength rejection characteristics and deep out-of-band blocking (≤0.03 %). Individual filters were mounted in a SBIG FW8S-STT filter wheel mounted below the STT-8300M camera. In addition, a single Hoya U-340 filter (25.4 mm diameter, 2 mm thickness) was mounted in a custom adapter within the filter wheel to be used for ‘standard’ signal detection analogous to current instrumentation. Total system transmittance was found to exceed 85% utilising the Astrodon SDSS filters (>80% for the SDSS u’2 ultraviolet filter), with approximately 70% transmittance when using the Hoya U-340 filter. The optical column and STT-8300M camera were interfaced to the RISO DA-15 automated luminescence reader by means of a custom mounting plate and turret adapter. The RISO unit is equipped with a 90Sr/90Y beta irradiation source and facilities for the thermal and optical stimulation of mineral grains, allowing repeated luminescence measurement from quartz samples. Multiple calibration and evaluation cycles were undertaken in developing the high-sensitivity multispectral thermoluminescence imaging system. The relative detection efficiency and system response was evaluated, with an investigation of the signal:noise ratio (SNR) between the CCD imaging system and the standard EMI 9235QB photomultiplier tube (PMT) arrangement used on the RISO DA-15 automated luminescence reader. The noise performance of the PMT arrangement exceeded that of the CCD-based imaging system, with approximately twice the SNR measured at all given doses. A marginal improvement (approximately 20%) was observed in the SNR when using the SDSS u’2 filter compared to the Hoya U-340 for the imaging system, and overall detection efficiency increased slightly at higher administered radiation doses. The system was used to successfully recover a known irradiation dose from a calibration quartz sourced from the RISO Denmark Technical University (DTU) National Laboratory. The clear delineation of the luminescence signal required the development of novel image processing techniques. An aperture photometry tool was used for signal intensity calculations; a method typically used to determine stellar magnitudes in astrophotometry. The software is designed to measure point-source intensity and its uncertainty by summing all pixel values within a constrained region-of-interest (i.e. the aperture) and subtracting the background contribution. This is estimated from a nearby imaged region that surrounds, but excludes, the observed radiance from the TL emission (i.e. the source signal). An innovative suite of imaging and analysis protocols were also developed to maximize signal collection efficiency in high-sensitivity luminescence imaging applications. The well-known effects of varying heating ramp temperatures as a means to increase signal intensity was investigated, along with the potential to shift TL peak position relative to the detection band constrained by the optical filter; thereby providing a further proxy to test system response and calibration. This method was further adapted to maximize clean photon yield in the narrow UV detection band, with overall photon yield shown to increase at lower ramp temperatures (below 1.0 °C s-1) for both large-aliquot and single-grain samples. System noise performance was improved with the development of a calibrated background correction, which suppressed the signal arising from blackbody radiation emitted by the heater plate of the RISO luminescence reader. Ultraviolet thermoluminescence (UV-TL) photon yield was compared between the industry-standard Hoya U-340 optical filter and the high-transmittance SDSS astrophotometry optical filter set. Exposure correction techniques to mitigate the thermal and readout noise associated with charge-transfer processes in CCD sensors were also investigated. These approaches are vital in maximizing signal collection efficiency and are a necessary precursor for the use of advanced imaging systems in routine luminescence dating applications. The multispectral thermoluminescence imaging system was then used to characterize the spectral signature of individual quartz grains, allowing the inter- and intra-sample spectral diversity of quartz grains from contrasting geological context to be analysed. Luminescence emission behaviour was characterised for quartz grains (180-212 μm) for three samples of contrasting geological context, from which spectral profiles were collated. A clear distinction in the spectral signatures of individual grains originating from single deposits were identified within each provenance. This is a key finding of the work undertaken; and represents a significant advance in the understanding of the spectral variation in TL emissions from quartz, as well as in the characterization of geological provenance for individual quartz grains through luminescence studies. By better understanding the full spectral signature of individual grains, information on specific trapping sites (through temperature-resolved signal peaks) and on recombination centres (through wavelength-resolved signal peaks) may be extrapolated. Such findings demonstrate not only the viable collection of the luminescence dating signal beyond the detection range of current commercial instrumentation, but also highlights the potential for thermoluminescence imaging technique to be developed as a routine dating method, providing a new approach for extracting valuable provenance information from mineral grains natively with the luminescence dating signal. A key set of challenges that must be overcome in bridging current detection and analysis methods with spatially-resolved luminescence imaging techniques is the ability to generate accurate and precise equivalent dose (De) estimates and dose distributions in quartz. An innovative suite of imaging and analysis protocols were developed, which allowed investigation into the multispectral dose-response behaviour for natural quartz samples. This allowed, for the first time, the ability to generate multispectral equivalent dose distributions for quartz using solid-state luminescence imaging techniques. Dose response curves and De estimates were successfully generated across all four detection bands under investigation; providing encouraging results for the efficacy and validity of the TL system and luminescence imaging methods presented herein. The dose estimates compared favourably with the independent known dose of the sample in the UV emissions band, with overestimation of De in other detection bands. The overestimation was attributed to extrinsic factors such as the functional differences in detection efficiency and noise performance of solid-state imaging systems, and intrinsic factors relating to luminescence production such as the kinetic behaviour of TL traps and colour centres in quartz. The latter factors relating to luminescence production may be addressed with the development of advanced luminescence imaging and analysis protocols, which seek to account for the variability in the spectral emissions from natural quartz samples. While the development of such comprehensive analysis protocols is beyond the scope of the present work, much of the success in attempting to bridge routine detection and analysis methods with spatially-resolved luminescence imaging techniques is reliant on the further development and optimization of such procedures. A single-grain method for generating De estimates for quartz supergrains using in-situ luminescence imaging techniques was also presented. This technique investigated the viability of extracting luminescence signals from extremely bright individual grains contained within large-aliquot samples. Dose response was found to vary considerably between grains, with large errors in signal intensity measures attributed to sub-optimal background subtraction parameters in dense-field imaging applications. Such artefacts serve to further highlight the need for a true single-grain luminescence imaging method, providing increased accuracy and precision in dose estimates compared to large-aliquot and in-situ luminescence measures. This was achieved by the present study. A single-grain De distribution was successfully generated in the red detection band using dose estimates from twenty-six individual grains, providing a central De value in good agreement of the known independent dose of the sample. However, single-grain TL dose distributions could not be generated in detection bands other than the red transmission window constrained by the SDSS r’2 optical filter. This was attributed to a combination of 1) instrument limitations; namely those relating to detection efficiency, noise performance and spectral resolution, 2) sub-optimality of analysis protocols for specific detection windows and routine dating, and 3) the complexity and variability of the kinetic response and recombination processes which give rise to TL spectra in natural quartz samples. These limitations may be addressed with improved automation and the use of single-photon sensitive, back-illuminated, UV-enhanced electron-multiplying charge-coupled device (EM-CCD) cameras with appropriate high-throughput custom optics. Such a system was devised by the Author as the subject of a funding proposal under the Australian Research Council (ARC) Linkage, Equipment, Infrastructure and Facilities (LIEF; LE180100148) grant scheme in 2018. This proposal is currently pending resubmission. The work contained in this thesis has made significant advances in geophotonics and the multispectral imaging of quartz thermoluminescence. Despite the considerable and complex challenges inherent to the process of instrument development, particularly within the temporal and financial constraints of a PhD project, this work has overcome significant challenges in moving toward the routine use of spatially-resolved imaging systems and techniques in luminescence dating applications. With ongoing research and improvements in these key areas, the use of solid-state detectors for routine signal collection and age determinations will prove an invaluable tool in luminescence dating applications.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:99/06632-0