A radioterapia é uma das três principais modalidades utilizadas no tratamento de doenças malignas como o câncer; as outras duas são a quimioterapia e a radiocirurgia. Em contraste com outras especialidades médicas que necessitam principalmente do conhecimento clínico e da experiência de especialistas, a radioterapia, com a utilização da radiação ionizante no tratamento do câncer, depende do investimento pesado em tecnologias modernas e dos esforços colaborativos de diversos profissionais, cuja equipe coordenada influencia, sobremaneira, o resultado do tratamento. A Radioterapia de intensidade modulada (IMRT) com o uso de colimadores multilâminas (multileaf collimators MLCs) tem o potencial para alcançar um alto grau de conformidade da dose no alvo (tumor a ser tratado) e ainda promover a proteção de tecidos normais do que a maioria de outras técnicas de tratamento, especialmente para volumes-alvo ou órgãos de risco com formatos complexos. Entretanto, estudos recentes mostraram que baixas doses de radiação podem causar tumores secundários. Esse trabalho tem como objetivo a determinação da distribuição de dose de radiação absorvida em diversas simulações de tratamentos radioterápicos com o uso de dosímetros compostos de LiF:Mg,Ti; CaSO4:Dy e Al2O3:C, utilizando um objeto simulador de polimetilmetacrilato (PMMA) empregando as seguintes técnicas dosimétricas: termoluminescência (TL), luminescência opticamente estimulada (OSL) e detectores semicondutores (diodos). / Radiotherapy is one of three principal treatment modalities used in the treatment of malignant diseases such as cancer; the other two are chemotherapy and radiosurgery. In contrast to other medical specialties that rely mainly on the clinical knowledge and experience of medical specialists, radiotherapy, with its use of ionizing radiation in treatment of cancer, relies heavily on modern technology and the collaborative efforts of several professionals whose coordinated team approach greatly influences the outcome of the treatment. Intensity modulated radiation therapy (IMRT) with the use of multileaf collimators (MLCs) has the potential to achieve a much higher degree of target conformity and normal tissue sparing than most other treatment techniques, especially for target volumes or organs at risk with complex shapes. However, recent studies show that low doses of radiation can cause secondary cancers. This work aims to determine the radiation dose distribution in several radiation therapy treatment simulations with use of LiF:Mg,Ti; CaSO4:Dy and Al2O3:C dosimeters using a PMMA phantom for the following dosimetry techniques: thermoluminescence, optically stimulated luminescence (OSL) and semiconductor detectors.

A radioterapia é uma das três principais modalidades utilizadas no tratamento de doenças malignas como o câncer; as outras duas são a quimioterapia e a radiocirurgia. Em contraste com outras especialidades médicas que necessitam principalmente do conhecimento clínico e da experiência de especialistas, a radioterapia, com a utilização da radiação ionizante no tratamento do câncer, depende do investimento pesado em tecnologias modernas e dos esforços colaborativos de diversos profissionais, cuja equipe coordenada influencia, sobremaneira, o resultado do tratamento. A Radioterapia de intensidade modulada (IMRT) com o uso de colimadores multilâminas (multileaf collimators MLCs) tem o potencial para alcançar um alto grau de conformidade da dose no alvo (tumor a ser tratado) e ainda promover a proteção de tecidos normais do que a maioria de outras técnicas de tratamento, especialmente para volumes-alvo ou órgãos de risco com formatos complexos. Entretanto, estudos recentes mostraram que baixas doses de radiação podem causar tumores secundários. Esse trabalho tem como objetivo a determinação da distribuição de dose de radiação absorvida em diversas simulações de tratamentos radioterápicos com o uso de dosímetros compostos de LiF:Mg,Ti; CaSO4:Dy e Al2O3:C, utilizando um objeto simulador de polimetilmetacrilato (PMMA) empregando as seguintes técnicas dosimétricas: termoluminescência (TL), luminescência opticamente estimulada (OSL) e detectores semicondutores (diodos). / Radiotherapy is one of three principal treatment modalities used in the treatment of malignant diseases such as cancer; the other two are chemotherapy and radiosurgery. In contrast to other medical specialties that rely mainly on the clinical knowledge and experience of medical specialists, radiotherapy, with its use of ionizing radiation in treatment of cancer, relies heavily on modern technology and the collaborative efforts of several professionals whose coordinated team approach greatly influences the outcome of the treatment. Intensity modulated radiation therapy (IMRT) with the use of multileaf collimators (MLCs) has the potential to achieve a much higher degree of target conformity and normal tissue sparing than most other treatment techniques, especially for target volumes or organs at risk with complex shapes. However, recent studies show that low doses of radiation can cause secondary cancers. This work aims to determine the radiation dose distribution in several radiation therapy treatment simulations with use of LiF:Mg,Ti; CaSO4:Dy and Al2O3:C dosimeters using a PMMA phantom for the following dosimetry techniques: thermoluminescence, optically stimulated luminescence (OSL) and semiconductor detectors.

This study was undertaken to compare the response of three dosimeters to different environments. Comanche Peak Nuclear Power Plant wants to replace the current badge of record. The RaDos DIS-1 direct-ion storage dosimeter (DIS-1) and the Landauer InLight optically stimulated luminescence dosimeter (OSL) are the two candidates for replacement of the Panasonic UD-802 thermoluminescence dosimeter (TLD). The dosimeters were compared in five categories: dose linearity, dose-rate linearity, fade response, humidity response, and the angular dependence of the dosimeters. The major results include verified linear relationship evidence for dose and doserate and a better fade response for both the DIS-1 and OSL. The TLDs faded by 9.2% over a month and the DIS-1 and OSL faded by 4.2% and 1%, respectively. Following a dose of 557.5 mrem, the dosimeters were exposed to different relative humidites. The dose to the DIS-1 and OSL did not change drastically while the TLDs dose readout was reduced by 10%. Finally, the angular dependence of the dosimeters was compared and the worst responses were 66% at 90° in the horizontal orientation for the OSL and 1.7% at 90° in the horizontal orientation for the DIS-1. Based on the results of these tests the OSL seems like a more viable candidate for the new badge or record.

Time Resolved OSL (TR-OSL) is a technique to record the luminescence decay curve data after a brief stimulation pulse and can possibly be used for the separation of luminescence signals from quartz and feldspars. In this study luminescence emission from quartz and feldspar samples was investigated. TR-OSL signals of these samples were studied for the variations with preheating and annealing temperature, stimulation pulse width and total stimulation time, optical bleaching, radiation dose and measurement temperature. TR-OSL decay lifetime of quartz samples was found as ~40 &micro / s. Na-feldspar and K-feldspar luminescence signals were deconvoluted using a linear sum of three exponential decays with lifetimes about 45 &micro / s, 8 &micro / s and 1 &micro / s and about 35 &micro / s, 7 &micro / s and 0.6 &micro / s, respectively. Since feldspars signals have a component with lifetime similar to that of quartz (~40 &micro / s), luminescence signal separation with TR-OSL seems to be not straightforward.

Optically Stimulated Luminescence (OSL) is the luminescence emitted from a previously irradiated insulator (or a wide band gap semiconductor) upon exposure to light. The OSL signal intensity is a function of the radiation dose absorbed by the sample and thus can be used as the basis of a radiation dosimetry method. In the literature, OSL studies on natural fluorites are rather limited. In order to promote the material for radiation dosimetry, OSL properties of natural fluorites of different origin were examined in this study. For this purpose, dose-response, reproducibility, thermal stability and fading of the OSL signals were analyzed. In order to find a relation between OSL and TL signals, TL signals and the effect of OSL measurements on TL signals were examined. Thermal activation energies of the light sensitive TL peaks and the OSL signals were also calculated using different methods and the results were compared. Also, absence of the thermal quenching was shown. Finally, TR-OSL signals were measured to have an opinion about the recombination centers. As a result of these studies, it is possible to conclude that natural fluorites show promising features to be used as an environmental dosimeter with regard to a suitable OSL signal, range of linearity, repeatability in response, as well as being readily available at a low cost.

Scanning electron microscope, X-ray diffraction and photoluminescence measurements were conducted on Be(x)Zn(1−x)O nanowires prepared by electrochemical and hydrothermal deposition to study their morphology, structure and optical properties. The bowing parameter for nanowires prepared by electrochemical and hydrothermal deposition was found to be 4.8 eV and 3.6 eV, respectively. It was observed that for electrochemical deposition, it is more difficult for Be(2+) to incorporate in the crystal lattice than Zn(2+). The electrochemical deposited samples exhibited stronger deep level emissions, indicating a higher density of deep level states. A home-made Optically Stimulated Luminescence (OSL) system was successfully constructed and calibrated with Al2O3:C and BeO. The OSL lifetime measurements on electrochemical deposited samples showed there were measurable OSL signals even on 500 nm long Be(x)Zn(1−x)O nanowires. The lifetimes of these OSL signals were found to decrease with increasing Be concentration. Be(x)Zn(1−x)O nanowires show considerable promise as new OSL materials.

Scanning electron microscope, X-ray diffraction and photoluminescence measurements were conducted on Be(x)Zn(1−x)O nanowires prepared by electrochemical and hydrothermal deposition to study their morphology, structure and optical properties. The bowing parameter for nanowires prepared by electrochemical and hydrothermal deposition was found to be 4.8 eV and 3.6 eV, respectively. It was observed that for electrochemical deposition, it is more difficult for Be(2+) to incorporate in the crystal lattice than Zn(2+). The electrochemical deposited samples exhibited stronger deep level emissions, indicating a higher density of deep level states. A home-made Optically Stimulated Luminescence (OSL) system was successfully constructed and calibrated with Al2O3:C and BeO. The OSL lifetime measurements on electrochemical deposited samples showed there were measurable OSL signals even on 500 nm long Be(x)Zn(1−x)O nanowires. The lifetimes of these OSL signals were found to decrease with increasing Be concentration. Be(x)Zn(1−x)O nanowires show considerable promise as new OSL materials.

Correlations between societal development and climate changes have been investigated for a long period of time. At the archaeological site of Beidha, southern Jordan, most studies have focussed on the Late Pleistocene/Holocene, however, the importance of the Beidha region may even reach further back in time. The presence of water in a generally very dry landscape would have been crucial to early modern humans en route from Africa to all other continents. Through sedimentological observations and OSL dating, this study aims to contribute to solving the puzzle of the local landscape development at Beidha during a longer time scale. It is suggested that a long period of calm floodplain conditions took place, approximately during periods of high lake levels in Lake Lisan ~70-21 ka. After that, a period of soil development has been identified between two phases of aeolian deposition. More recently, during the Holocene, phases of mass flow events may have affected the area.

At the turn of the century, Kanab Creek incised 30-meters into its alluvium, leaving behind fluvial terraces and thick basin fill sediments exposed along arroyo walls. Research objectives were to determine the timing and causes of past valley-filling and arroyo-cutting episodes along a 20 km-long reach of Kanab Creek in southern Utah. Fluvial deposits were mapped at the 1:12,000 scale and sediments were described and dated using Optically Stimulated Luminescence (OSL) and radiocarbon dating. The Kanab Creek valley can be divided into a narrow, upper terraced reach and a broad lower basin fill reach near Kanab, Utah. The most prominent terrace in the upper reach is Quaternary alluvial terrace 4 (Qat4), followed by Qat3, Qat2/3, and Qat2 map units. These are composed of tabular-bedded, fine-grained sand, silt, and clay layers. The Qat2/3 map unit is a both a fill and fill-cut terrace underlain by Qa4, Qa3, and Qa2 alluvium and is used when the Qat3 fill-cut (fill-strath) terrace can not be differentiated from the Qat2 fill terrace due to their similar geomorphic position. The Qat3 fill-cut terrace upstream correlates to ~8 meters of aggradation downstream. The youngest terrace, Qat1, is a minor terrace, composed of coarse-grained channel facies. More recent channel and floodplain deposits were deposited over the last century following arroyo cutting. OSL and radiocarbon results suggest at least four cycles of fluvial cutting and filling: >6-3.5ka (Qa4), ~3->1ka (Qa3), 0.7-0.12ka (Qa2), and post-1880 AD (Qa1). Correlation to regional climate records suggests major periods of aggradation correlate to regionally cooler and wetter climatic intervals. Periods of arroyo cutting occurred at >6ka, ~3ka, 1-0.7ka, and during historic arroyo cutting (1882-1914 AD), and correlate to regionally warmer, drier intervals. These periods of aggradation and incision are roughly contemporaneous with regional drainages, except for the large aggradation seen in Kanab Creek 6-3.5ka (Qa4). Analysis of terrace longitudinal profiles indicates Qat4 has the lowest concavity suggesting that Qat4 aggraded during a period of greater sediment supply and/or reduced flood regime. Although OSL samples exhibited some degree of incomplete zeroing, calculated ages using a minimum age model are consistent with radiocarbon results.

De nombreuses tentatives de reconstruction de l’étendue du paléo-pergélisol à partir de données de terrain montrent que de grandes parties de la France ont été affectées à la fin du Pléistocène. Cette étendue maximale a été attribuée au Dernier Maximum Glaciaire (DMG). Néanmoins, des contradictions existent entre les différentes reconstructions qui ont été réalisées pendant près d’un siècle ; elles résident en partie dans l’absence de consensus sur la signification paléoclimatique de certaines structures périglaciaires. De plus, le cadre chronologique utilisé pour ces reconstructions est principalement basé sur des datations relatives et/ou sur l’hypothèse que le maximum de froid durant le dernier glaciaire a été atteint pendant le DMG. Dans ce contexte, il était nécessaire de réévaluer les structures déjà décrites à la lumière de notre connaissance actuelle des processus périglaciaires et d’en chercher de nouvelles pour datation. L’approche développée pour résoudre ces problèmes a été divisée en trois parties. Tout d’abord, une base de données homogène fournissant un accès simple aux structures périglaciaires répertoriées sur le territoire français a été constituée. Celle-ci permet de remettre un site ou une structure dans un contexte régional pour éviter les interprétations simplistes et favorise une vision à l’échelle nationale. Cette base de données est accessible en ligne (https://afeqeng.hypotheses.org/48). Les données en coupe concernant les coins sableux, les pseudomorphoses de coin de glace et les coins composites ainsi que les données obtenues à partir de photos aériennes sur les polygones et les sols striés ont été compilées. Dans la deuxième partie de notre travail, nous nous sommes attachés à traiter les données recueillies. L’analyse à l’aide d’un SIG nous a apportée des informations sur l’influence de différents facteurs sur le développement des structures périglaciaires. Des comparaisons avec un ensemble de données du Nord de l’Europe a rendu possible la proposition d’une nouvelle carte des limites du pergélisol lors de son extension maximale en Europe de l’Ouest. La carte a ensuite été comparée avec des simulations du pergélisol issues de Modèles Globaux du Climat. Enfin, la troisième partie de cette thèse fournit le premier cadre chronologique pour la fissuration par contraction thermique du sol en France, en s’appuyant sur la datation par luminescence optiquement stimulée (OSL) du remplissage sableux des coins. / During the Mid to Late Pleistocene, the land area affected by periglacial conditions expanded and contracted repeatedly over large surfaces in mid-latitude Western Europe. In such environments, permafrost or deep seasonal freezing of the ground formed typical features, which have been the subject of abundant research by geomorphologists. In particular, researchers attempted to reconstruct the maximal extent of Pleistocene permafrost based on field evidence. Although most reconstructions suggest that permafrost spread over part of France during the coldest periods of the Pleistocene, there is no agreement regarding the land surface affected. This is mainly due to the scarcity of field data used for mapping and to the questionable palaeoclimatic significance of certain periglacial features. In addition, permafrost modelling during the Last Glacial Maximum using Global Climate Models does not seem consistent with field data. To solve these issues, a database of Pleistocene periglacial features has been compiled from a review of academic literature and unpublished reports, the analysis of aerial photographs and new field surveys. Polygons, soil stripes, ice-wedge pseudomorphs, sand wedges and composite wedge pseudomorphs were included in the database together with their geographic coordinates, geological context, description and references. The distribution of the identified features was analysed with a GIS software and clearly indicates that large areas in France were affected by periglaciation, apart from the southwesternmost part of France and the Languedoc. Ice-wedge pseudomorphs do not extend south of 47°N which indicates that widespread discontinuous permafrost did not affect the land south of the Paris basin. The exclusive presence of sand wedges with primary infill between 45 and 47°N, mainly in the periphery of coversands, suggests that thermal contraction cracking of the ground occurred together with sand drifting in a context of deep seasonal frost or sporadic discontinuous permafrost, unfavourable for the growth of significant ground-ice bodies. However, the description of composite-wedge pseudomorphs below 47°N indicates that at least locally ice veins formed probably during exceptionally cold winters. To provide a chronological framework for thermal contraction cracking single-grain OSL measurements were performed on 33 samples taken in the sandy infilling of sand-wedges and composite-wedge pseudomorphs. Results suggest that multiple events were recorded within wedges. The extraction of the datasets using the Finite Mixture Model, which was developed to analyse statistically data comprising multiple components, allowed calculating 86 ages. These age estimates show that wedge activity in France occurred at least 11 times over the last 100 ka. The most widespread events of thermal contraction cracking occurred between ca. 30 and 24 ka (Last Permafrost Maximum) and are concomitant with periods of high sand availability (MIS 2). Although most phases of sand-wedge growth correlate well with known Pleistocene cold periods, the identification of wedge activity during late MIS 5 and the very beginning of the Holocene strongly suggests that sand-wedges do not only indicate permafrost but also deep seasonal ground freezing in the context of low winter insolation. The previously published young ages yielded by North-European sand-wedges likely result from poor record of periglacial periods concomitant with low sand availability and/or age averaging inherent to standard luminescence methods. This work allowed us to propose a map of the maximum extent of Late Pleistocene permafrost in France, which partially reconciles field data with palaeoclimatic simulations. The remaining discrepancies may be linked with a potential time lag between the Last Permafrost Maximum (c. 31–24 ka) and the Last Glacial Maximum (21 ka) and to the already identified warm winter bias of the models.