The reflection of the X-rays emitted from a corona of energetic particles surrounding an accreting black hole from the accretion disc is investigated in the context of probing the structure of the central regions as well as the physical processes that power some of the brightest objects seen in the Universe. A method is devised to measure the emissivity profile of the accretion disc, that is the reflected flux as a function of radius in the disc. This method exploits the variation in the Doppler and gravitational redshift of emission from different radii in the disc to fit the observed reflection spectrum as the sum of contributions from successive radii and is applied to X-ray spectra of the narrow line Seyfert 1 galaxies 1H 0707-495, IRAS 13224-3809 and MCG-6-30-15 as well as the Galactic X-ray binary, Cygnus X-1. This illumination pattern of the accretion disc is a sensitive probe of the geometry of the corona that is illuminating the disc. A formalism is developed in which systematic ray tracing simulations can be run between X-ray emitting coronae and the accretion disc for a range of source geometries and other physical parameters, allowing observable data products to be simulated that can be directly compared to data from astrophysical black holes, in order to determine how these parameters affect the observed data, allowing them to be constrained observationally. The measured emissivity profiles are found to be in agreement with those expected theoretically and it is also discovered that the measured emissivity profile can be used to determine the radial extent of the X-ray emitting corona above the accretion disc. The X-ray emitting coronae are located and their radial extents constrained in 1H 0707-495, IRAS 13224-3809 and MCG-6-30-15, while the insight gained into accretion disc emissivity profiles from ray tracing simulations allows the low flux state that 1H 0707-495 was seen to drop in to in January 2011 to be explained in terms of a collapse of the X-ray emitting corona to a confined region around the central black hole. The rapid variability of the X-ray emission from accreting black holes is exploited in the use of reverberation time lags, where variability in the continuum is seen to lead that in its reflection from the accretion disc, to measure the distances between the X-ray emitting corona and the reflector. Ray tracing calculations are developed to simulate lag spectra that can be measured in X-ray observations to provide a means of constraining the extent and geometry of the corona, complimentary to the use of the emissivity profiles. Combining these methods, the X-ray emitting coronae are constrained to extend radially outward a few tens of gravitational radii over the accretion disc, while extending vertically a few gravitational radii above the plane of the disc. Furthermore, it is demonstrated how measured lag spectra can be used to understand the propagation of luminosity fluctuations through the extent of the corona and techniques are developed for analysing energy-resolved variability analysis that will be possible with future generations of X-ray telescopes. Finally, these methods, along with theoretical insight gained form ray tracing simulations, are applied to X-ray spectra extracted from 1H 0707-495 during periods of low and high flux during the observations. Evidence is found for the expansion of the corona along with a drop in the average energy density as the X-ray luminosity increases followed by its contraction as the luminosity decreases on timescales of hours.

The wide-area XMM-XXL X-ray survey is used to explore the fraction of obscured active galactic nuclei (AGNs) at high accretion luminosities, L-X(2-10 keV) greater than or similar to 10(44) erg s(-1), and out to redshift z approximate to 1.5. The sample covers an area of about 14 deg(2) and provides constraints on the space density of powerful AGNs over a wide range of neutral hydrogen column densities extending beyond the Compton-thick limit, N-H approximate to 10(24) cm(-2). The fraction of obscured Compton-thin (N-H = 10(22) - 10(24) cm(-2)) AGNs is estimated to be approximate to 0.35 for luminosities L-X(2-10 keV) > 10(44) erg s(-1), independent of redshift. For less luminous sources, the fraction of obscured Compton-thin AGNs increases from 0.45 +/- 0.10 at z = 0.25 to 0.75 +/- 0.05 at z = 1.25. Studies that select AGNs in the infrared via template fits to the observed spectral energy distribution of extragalactic sources estimate space densities at high accretion luminosities consistent with the XMM-XXL constraints. There is no evidence for a large population of AGNs (e.g. heavily obscured) identified in the infrared and missed at X-ray wavelengths. We further explore the mid-infrared colours of XMM-XXL AGNs as a function of accretion luminosity, column density and redshift. The fraction of XMM-XXL sources that lie within the mid-infrared colour wedges defined in the literature to select AGNs is primarily a function of redshift. This fraction increases from about 20-30 per cent at z = 0.25 to about 50-70 per cent at z = 1.5.

Estimates of left atrial size in patients with suspected cardiac disease play an important role in diagnostic medicine. Left atrial size is used in predicting prognosis and events, as well as treatment decisions. Two methods are commonly used to estimate left atrial size: chest radiography and cardiac ultrasound. This study aims to determine the test characteristics of chest radiography and compare the use of radiographs to cardiac ultrasound (the gold standard test). Data from patients older than 18 years admitted to Pretoria Academic Hospital during 2000-2003 who had both chest X-rays and cardiac ultrasound were included in this cross-sectional, retrospective analysis. Chest X-rays were classified into three quality classes, and the sub-carinal angle (SCA) and sub-angle distance (SAD) were measured twice in all available X-rays by two observers. Intra- and interobserver variability (3 methods) as well as the predictive value of the SCA and SAD measurements were determined using logistic regression (with left atrial size determined by ultrasound as comparator). P-values < 0.05 were regarded as statistically significant for all comparisons. Data for 159 patients were available (154 cardiac ultrasounds and 178 chest radiographs). Intraobserver variability regarding chest X-ray measurements was low with almost perfect concordance (P=0.000). Interobserver variability was higher for supine X-rays. Using logistic regression, a linear model was identified which was statistically significant only for erect X-rays. While goodness-of-fit analysis showed that the model fits the data, performance characteristics were poor, with high sensitivity and low specificity, and an area under the ROC curve of 0.62-0.63, depending on type of X-ray and measurement (SCA or SAD). Linearity in the logit of the dependent variable was assessed, and found to be present at the extremes of carinal angle measurements for the supine X-ray data and in the first three quartiles for erect X-ray data. A non-linear model determined by fractional polynomial analysis did not perform significantly better than the original linear model. Cut-off values for the SCA of 72o and 84o (erect and supine X-rays, respectively) were found to give the best compromise between sensitivity and specificity. The corresponding cut-off values for SAD were 24.1mm and 26.9mm. Assessment of either SCA or SAD to determine left atrial size is equivalent and repeatable, both within the same observer, and between two observers (less so for supine X-rays). While this measure is precise, it was found not to be very accurate. Therefore, chest X-rays are not reliable in predicting left atrial enlargement. / Dissertation (MSc (Clinical Epidemiology))--University of Pretoria, 2007. / Clinical Epidemiology / unrestricted

Orientadores: Lisandro Pavie Cardoso, Rossano Lang Carvalho / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T10:35:30Z (GMT). No. of bitstreams: 1 CalligarisdeAndrade_Guilherme_M.pdf: 21575111 bytes, checksum: b393b34194bc7dab77ca356bced5b375 (MD5) Previous issue date: 2014 / Resumo: O alto controle e reprodutibilidade envolvidos nas técnicas de implantação e de irradiação iônica fazem com que elas sejam muito utilizadas por permitir modificação estrutural de semicondutores, possibilitando, por exemplo, a geração de defeitos estruturais que atuam como centros de recombinação radiativa de portadores para aplicação em eficientes dispositivos emissores de luz baseados em Silício. Igualmente necessária é a caracterização estrutural desses materiais modificados, como os sistemas provenientes de engenharia de defeitos, promovendo um correto e abrangente entendimento que irá contribuir para a otimização dos seus processos de síntese. Nesse contexto, e motivados por resultados recentes, o presente trabalho visa aplicar técnicas de raios-X com boa resolução no estudo de defeitos gerados pelos processos de implantação e irradiação em dois sistemas distintos baseados em Silício. O primeiro sistema, em que amostras de Si(001) foram implantadas com Fe+ e irradiadas com Au++, mostrou uma forte absorção na região de UV (maior para a amostra implantada e irradiada) durante seus estudos preliminares de reflectância óptica UV-Vis. O segundo, em que amostras de Si(001) implantados com Xe+ e submetidas a posterior tratamento térmico de 600, 700 e 800 ºC/30 min, foi motivado por trabalhos do grupo de pesquisa do Laboratório de Implantação Iônica - UFRGS, em que íons de He e Ne produziram nanobolhas no Silício monocristalino. Foram utilizadas as técnicas de Refletividade de Raios-X (XRR), Difração de Raios-X com Incidência Rasante (GIXRD), além de varreduras no espaço recíproco Q-scans e Mapeamentos do Espaço Recíproco (RSM) que utilizam geometria de alta resolução. Também foram realizadas varreduras Renninger e mapeamentos ?:?, ângulos incidente (?) e azimutal (?) acoplados, da Difração Múltipla de Raios-X (XRMD) utilizando Radiação Sincrotron. A Fluorescência de Raios-X (XRF) e a Microscopia Eletrônica de Transmissão (TEM) também foram utilizadas como técnicas complementares. Os resultados do primeiro sistema (Fe+/Au++) para a XRR distinguiu as diferentes regiões geradas pelos processos de implantação/irradiação de íons. A análise das amostras implantada e irradiada e a apenas irradiada foi feita: i) por medidas de Q-scan para a reflexão (004) e mostrou a contribuição de uma região distorcida (RD) na direção normal à superfície com a? = 5,4235(4) Å, com perfil diferente para cada uma delas; ii) por RSM e mostrou contribuições diferentes no padrão de intensidade, na direção QX (direção paralela), para essas mesmas amostras; iii) por mapeamentos ?:? da XRMD na exata condição de 4-feixes (000)(002)(1 1 1)(1 13) e mostrou a ocorrência inédita, para este sistema, de um pico de reflexão híbrida coerente (CHR) do tipo substrato/camada (SL), envolvendo o caminho (1 13)S + (11 1)L . Os resultados do segundo sistema (Xe+) para medidas de: i) RSM e ii) Q-scans com a reflexão assimétrica (113) da amostra como-implantada mostraram a contribuição dos defeitos pontuais gerados pela implantação. Nas amostras tratadas termicamente mostraram a recristalização da rede do Si com o tratamento térmico (direção perpendicular), além de evidenciar a formação de uma região tensionada com a? = 5,425(2) Å (800 ºC/30 min); iii) mapeamento ?:? mostraram o aumento da densidade de defeitos com a temperatura de recozimento, tanto pelo espalhamento difuso no caso 3-feixes (000)(002)(1 11) , quanto pela ocorrência de extinção primária no caso 4-feixes (000)(002)(1 1 1)(1 13) . Imagens de seção transversal (TEM) em associação com análise elementar por Espectroscopia de Energia Dispersiva (EDS) confirmaram a presença de nanodefeitos, possivelmente do tipo {111} e {113}, e a formação de nanobolhas de Xe, que por sua vez devem ser os responsáveis pela tensão compressiva observada por RSM / Abstract: The high reproducibility and control involved in ion implantation and irradiation techniques, makes them to be widely used to allow structural modification of semiconductors, enabling, for instance, the generation of structural defects that act as radiative recombination centers of carriers for application in efficient Silicon-based light emitting devices. Equally necessary is the structural characterization of these modified materials, such as engineered-defects systems, promoting an accurate and comprehensive understanding that will contribute to the optimization of their synthesis processes. In this framework, and motivated by recent results, the present work intends to apply highresolution X-ray techniques on the study of the defects created by ion implantation/irradiation process into two distinct Silicon-based systems. The first system consists of Fe+-implanted and/or Au++-irradiated Si(001) samples that exhibited a significant absorption increase on the UV region during preliminary studies of its UV-Vis optical reflectance. The second system consists of Xe+- implanted Si(001) samples thermally treated at 600, 700, and 800 ºC/30 min, that was motivated by previous works from Laboratório de Implantação Iônica ¿ UFRGS in which He and Ne ions have produced nanobubbles in a Silicon matrix. The X-ray techniques, such as Reflectivity (XRR), Grazing Incidence (GIXRD), and also Qscans on reciprocal space and Reciprocal Space Mappings (RSM), under high-resolution geometry, were all used in the measurements. Furthermore, Renninger scans and X-Ray Multiple Diffraction (XRMD) ?:? mappings, for coupled incident (?) and azimuthal (?) angles, were also applied with synchrotron radiation. X-Ray Fluorescence (XRF) and Transmission Electron Microscopy (TEM) were employed as complementary techniques. For the first system (Fe+/Au++), XRR results were able to distinguish the distinct regions generated by the ion implantation/irradiation process. The analysis of the implanted-and-irradiated sample, as well as the just irradiated sample was made by: i) Q-scans of the (004) reflection and exposes the contribution of a Distorted Region (RD) in the out-of-plane direction with a? = 5.4235(4) Å, which has a different profile for each sample; ii) RSM that reveals distinct QX (inplane direction) intensity profiles for each sample; iii) ?:? mapping of the XRMD at the exact condition of the (000)(002)(111)(113) 4-beam case that exhibited an unprecedented occurrence, for this system, of a Coherent Hybrid Reflection (CHR) peak involving the substrate/layer (SL) S (1 13) + L (11 1) path. The results of the second system (Xe+) for the measurements of: i) RSM and ii) Q-scans using the asymmetric (113) reflection of the as-implanted sample showed the contributions of the implantation-induced point defects. The annealed samples have exposed the Si lattice recrystallization (out-of-plane profile), in addition to demonstrating the formation of a strained region with a? = 5.425(2) Å (800 ºC/30 min); iii) ?:? mappings showed an increase of defects density for higher temperature annealed samples by both the diffuse scattering in the (000)(002)(111) 3-beam case, as the occurrence of primary extinction for the (000)(002)(111)(113) 4-beam case. The presence of both {111} and {113} defects, as well as Xe nanobubbles formation, were confirmed by cross-section TEM images in association with elemental analysis by Energy Dispersive Spectroscopy (EDS), indicating that the later one is responsible for the compressive strain observed by RSM measurements. Combined cross-section TEM images and Energy Dispersive Spectroscopy (EDS) results have confirmed the presence Xe nanobubbles, which should be responsible for the compressive strain observed by RSM measurements, as well as the formation of the {111} and {113} nanodefects / Mestrado / Física / Mestre em Física

Orientador: Antonio Jose Ramirez Londono / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-26T15:15:59Z (GMT). No. of bitstreams: 1 Faria_GuilhermeAbreu_M.pdf: 7344692 bytes, checksum: e531c95d64110532e988972471c0e25d (MD5) Previous issue date: 2014 / Resumo: O objetivo deste trabalho foi desenvolver a metodologia de medição e análise de dados para a instalação experimental XTMS. Esta instalação foi projetada para possibilitar a medição simultânea de difração de raios X e informações térmicas e mecânicas de materiais enquanto estes são submetidas a condições termomecânicas controladas. Esta é uma área de grande interesse para cientistas de materiais uma vez que uma vasta gama de propriedades termomecânicas têm suas origens em propriedades microscópicas que são acessíveis através de dados de difração. Durante o trabalho, foram estudadas estratégias de medição, desenhos de amostras, métodos de processamento e análise de dados, assim como foi feita a caracterização da instalação como equipamento de medida de dados de difração. Como parte do trabalho, a instalação foi aplicada no estudo de casos científicos de interesse, que envolvem tanto diferentes metodologias de ensaios quanto dados de difração que exigem diferentes metodologias de análise. Os estudos consistiram em um ensaio de deformação em uma liga com memória de forma, ensaios de decomposição isotérmica em um aço inoxidável Superduplex UNS-S32750, e um ensaio de dilatometria acompanhado por difração do aço supermartensítico SuperCr13 / Abstract: The aim of this work was to develop measurement and data analysis methodologies for the XTMS experimental installation. This facility was engineered to simultaneously collect X-ray diffraction and thermo-mechanical information of materials as they are subjected to controlled thermo-mechanical conditions. This is an area of great interest for material scientists given the wide range of thermo-mechanical properties correlated with microscopic properties which are accessible through X-ray diffraction. Developments performed during this work include the development and/or study of measurement strategies, sample designs, and data processing and analysis, as well as the characterization of the XTMS installation as an X-ray diffraction station. As part of the work, the installation was used to study several cases of scientific interest, involving different testing and data analysis methodologies. The studies performed were the deformation of a shape memory alloy, the isothermal ferrite decomposition on a Superduplex stainless steel UNS-S32750, and phase transformations on a SuperCr13 supermartensitic steel through dilatometry coupled with time resolved X-ray diffraction / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientador: Lisandro Pavie Cardoso / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-30T18:16:34Z (GMT). No. of bitstreams: 1 Freitas_HugoEugeniode_M.pdf: 2201633 bytes, checksum: 992e7c3d4fcb71e7f0d75a25eba2bb39 (MD5) Previous issue date: 2016 / Resumo: No presente trabalho estudou-se a diferença entre dois tratamentos térmicos realizados em amostras de Si(111) implantadas com íons Cr+, utilizando-se a difratometria de raios X para policristais e a refletividade de raios X, assim como, curvas de rocking e difração múltipla de raios X usando radiação sincrotron que são aplicadas aos monocristais. O tratamento térmico posterior das amostras resulta numa melhoria da qualidade cristalina, mas leva à formação de trincas e extensos defeitos, devido à grande diferença na expansão térmica entre siliceto e silício pelas altas tensões induzidas. Portanto, há um grande interesse tecnológico na obtenção de camadas contínuas de alta qualidade com um mínimo de distorções induzidas no substrato. Esta é a motivação do presente trabalho: obter camadas finas de CrSi2 de alta qualidade cristalina na subsuperfície de substratos Si(111) e com o mínimo de deformações na matriz hospedeira usando implantação de íons a baixa energia. Serão explorados dois distintos tipos de tratamentos térmicos: o recozimento tradicional a vácuo em forno do tipo mufla (FA - furnace annealing) e o recozimento térmico rápido (RTA - rapid thermal annealing) em atmosfera de argônio. A formação da fase semicondutora hexagonal do CrSi2 foi confirmada por difratometria de raios X nas amostras tratadas termicamente e mostrou uma melhor qualidade cristalina obtida no recozimento FA. O modelo proposto de uma camada superficial de SiO2 fina (8?2) nm sobre uma ou duas camadas de CrSi2 (21?5) nm acima do substrato de Si(111) foi confirmado, a partir das medidas de refletividade de raios X, que também permitiu observar a maior difusão dos íons de Cr+ na amostra tratada com FA por maior tempo. Devido a este tratamento térmico promover, a altas temperaturas, uma maior difusão dos íons implantados, concluiu-se que o tratamento térmico mais propício para a fabricação de semicondutores baseados em CrSi2 é o tratamento por RTA. Varreduras Renninger obtidas da difração múltipla de raios X mostraram que a implantação de Cr+ em Si(111) e posterior recozimento não induz alteração de simetria nas amostras, apenas uma pequena relaxação da distorção tetragonal detectada para a amostra 800º C com tratamento FA. Mapeamentos acoplados dos ângulos de incidência (?) e azimutal (?) para a condição exata de reflexões secundárias Bragg-Superfície (BSD) da difração múltipla não permitiram detectar modificações estruturais de superfície nas amostras analisadas, após os dois tratamentos térmicos a 800º C que foram considerados / Abstract: In this work, the effect of the two heat treatments suffered by Si(111) samples implanted with Cr+ ions has been studied by means of X rays powder diffraction and X rays reflectivity, as well as, the single crystal techniques rocking curves and synchrotron X rays multiple diffraction. The heat treatment of the samples subsequent to the implantation results in an improved crystal quality, but leads to cracks formation and extensive damage due to the large difference between the thermal expansion coefficients of silicide and silicon induced by the applied high voltages. Therefore, there is a great technological interest in obtaining high quality continuous layers with a minimum induced distortion into the substrate. This is the motivation of the present work: to obtain CrSi2 thin layers of high crystalline quality in the subsurface of Si(111) substrates with minimal deformations in the host matrix using low energy ion implantation. Two distinct thermal treatments are analyzed: traditional annealing in vacuum oven muffle type (FA - furnace annealing) and rapid thermal annealing (RTA - rapid thermal annealing) in argon atmosphere. The formation of the semiconductor CrSi2 hexagonal phase was confirmed by X ray powder diffraction in the annealed samples that has also shown an improved crystalline quality observed in FA annealing process. The proposed model of a thin (8?2) nm SiO2 surface layer on top of one or two (21?5) nm thick CrSi2 layers above the Si(111) substrate was confirmed from the X ray reflectivity measurements, that has also allowed to observe further diffusion of Cr + ions into the sample implanted and FA annealed for a longer time. Since this heat treatment promotes, at high temperatures, a greater diffusion of the implanted ions, it was found that RTA is the most suitable treatment for the fabrication of semiconductor-based CrSi2. Renninger scans of the X ray Multiple Diffraction have shown that the Cr+ ions implantation in Si(111) process with a subsequent annealing does not induce symmetry change in the samples, just a small relaxation of the tetragonal distortion detected for the 800 ºC sample after FA treatment. Mappings of the incidence (?) and azimuthal (?) coupled angles monitoring the exact multiple diffraction condition for the Bragg-Surface Diffraction (BSD) secondary reflections were not able to detect structural changes along the analyzed samples surfaces, after the two distinct annealed processes considered at 800º C / Mestrado / Física / Mestre em Física / 132986/2014-0 / CNPQ

Quantum materials have strong electron correlation effects. According to the “structure-property” relationship, it is crucial to study the structure of quantum materials to better understand and manipulate the physical properties. The quantum effects are significant at the atomic microscopic length scale, which is not feasible to be studied by the average long-range structure measurement from conventional diffraction methods. Instead the local structure probe, pair distribution function (PDF) analysis, can effectively reveal the mystery of local structure, which is sensitive to the local behavior rather than the bulk average properties. In this thesis, the joint neutron and x-ray PDF (NXPDF) method is implemented. Because of their different interactions with matters, a combination of neutron and x-ray scattering can help comprehensively understand the atomic structures of some strongly correlated d- and f-electron systems that are difficult to be studied alone. Though powerful for understanding the structure of complex materials, performing the PDF modeling and structure refinement usually requires a lot of work on model selection for candidate structures. To address this problem, a new approach is developed to obtain candidate atomic structures from NXPDF, called structure-mining, in a highly automated way. It fetches, from open structural databases, all the structures meeting the experimenter's search criteria and performs structure refinements on them without human intervention. Tests on various material systems show the effectiveness and robustness of the algorithm in finding the correct atomic crystal structure. It works on crystalline and nanocrystalline materials including complex oxide nanoparticles and nanowires, low-symmetry and locally distorted structures, and complicated doped and magnetic materials. The examples of applying structure-mining method to identify the local structures of Pr₆O₁₁, BaFeₓTi₁−ₓO₃, and MgTi₂O₄ materials, which have strongly correlated 𝓭- and 𝑓-orbital electronic states under study in the thesis, are shown as well. This approach could greatly reduce the traditional structure searching work for quantum materials as well as other systems. The NXPDF method is first applied to the praseodymium oxide semiconductor nanoparticles to investigate the local structure behavior accompanied by the loss of electrical conductivity when temperature changes. The Pr and O sublattices can be determined precisely by x-ray and neutron PDF, respectively, because of their distinct x-ray atomic form factors and neutron scattering lengths. A combination of a highly ordered structure motif and a locally distorted oxygen deficient structure environment can describe the measured NXPDFs reasonably well. The iron doped barium titanate BaFeₓTi₁−ₓO₃ system is also investigated using PDF methods for studying the multiferroic behavior in the nanocrystals, which are synthesized near room temperature. The perovskite structure is established to be non-centrosymmetric, consistent with predictions of the pseudo-Jahn-Teller effect being the underlying cause of off-center displacements of B-site (Ti and doped Fe) atom, lowering the symmetry in order to make additional overlap between the 3d orbital of Ti and neighboring O atoms to create π molecular orbitals. This triggers the spontaneous polarization of the crystal. The PDF results establish that Fe is successfully doped into the ferroelectric BaTiO₃ phase, and the measured dielectric and magnetic properties also validate the multiferroic behavior of the synthesized BaFeₓTi₁−ₓO₃ nanocrystals. In addition, the NXPDF analysis is also conducted on the MgTi₂O₄ system to track the evolution of the local atomic structure across the temperature-dependent metal-insulator transition, and the results reveal that local tetragonality is persistent, preformed with reduced magnitude, deep in the metallic and on average cubic regime. Significantly, the high temperature local state revealed by PDF is not continuously connected to the orbitally ordered band insulator ground state and the transition cannot be characterized as a trivial order-disorder type. The shortest Ti-Ti bond lengths corresponding to spin singlet dimers shift to longer distances on warming but are still shorter than those seen in the cubic average structure. These seemingly conflicting observations could be reconciled within the model of a local fluctuating t₂g orbital-degeneracy-lifted (ODL) precursor state. These results undoubtedly establish the effectiveness of the joint neutron and x-ray PDF analysis to investigate the structure-property relationship on the sub-nanometer length scale of strongly correlated electron materials, utilizing the complementary structure information obtained from neutron and x-ray scattering.

La diffusion Compton inverse est un moyen unique pour produire des rayons X quasi-monochromatiques via l'interaction entre des électrons relativistes et une impulsion laser. Ce processus présente l'avantage de produire des flux très élevés de rayons X avec des énergies supérieures à quelques dizaines de keV. De plus, la divergence du faisceau de sortie est beaucoup plus grande que dans les sources de lumière synchrotron classiques et le faisceau de rayons X est donc plus facile à manipuler. Nous présentons une source de rayons X en construction à l'Université Paris-Sud, ThomX. Cette source utilise un faisceau d'électrons de 50 MeV qui interagit à 16,7 MHz avec une impulsion laser de quelques picosecondes dont la puissance moyenne est à l'état de l'art avec 600 kW, permettant de produire des rayons X entre 30 et 50 keV avec un flux de 10^{13} ph/s. Cette gamme d'énergie ainsi que la dépendance énergie-angulaire provenant du processus physique conviennent aux applications sociétales comme la radiothérapie ou l'histoire de l'art.Une cavité optique de très haute finesse (> 24000) est utilisée comme prototype pour effectuer des travaux de R&D pour la source ThomX. 400 kW de puissance laser moyenne ont été stockés avec succès dans cette cavité, en utilisant un faisceau laser d'entrée de seulement 40 W. Ce résultat, unique au monde, permet d'envisager l'achèvement de la source de rayons X de faible coût et de haut flux ThomX. Cette thèse explique les études expérimentales et analytiques qui ont été réalisées pour atteindre cette performance, dont une généralisation du processus d'empilement des impulsions laser pour les faisceaux laser ayant une fréquence de répétition différente de celle de la cavité, et les méthodes développées pour l'amélioration expérimentale du couplage spatial. / Inverse Compton Scattering provides a unique way to produce quasi-monochromatic X-rays via the interaction of relativistic electrons with a laser pulse. This process has the advantage of producing very high fluxes of X-rays with energies above a few tens of keV. In addition the output beam divergence is much larger than in classical synchrotron light sources and the X-ray beam is thus easier to manipulate. We present an X-ray source under construction at Paris-Sud University, ThomX. This source uses a 50 MeV electron beam that collides at 16.7 MHz with a few picoseconds pulsed laser beam whose power is enhanced at the state of the art 600 kW average power to produce X-rays between 30 and 50 keV with a flux of 10^{13} ph/s. This energy range as well as the energy-angular dependence coming from the physical process are suitable for societal applications like radiotherapy or art history.A very high finesse optical cavity (> 24000) is used as a prototype to perform R&D for the ThomX source. 400 kW of average laser power have been successfully stored in this cavity, using an input laser beam of only 40 W. This result, unique in the world, is a pathway towards the completion of the low-cost, compact, high flux X-ray source ThomX. This thesis explains the experimental and analytical studies that have been performed to reach this performance, including a generalization of the process of laser pulse stacking to frequency-detuned laser beams, and the methods developped for experimental spatial coupling enhancement.

Effectuer des mesures de polarimétrie des rayons X provenant de sources astrophysiques permettrait d’obtenir de nombreuses informations sur les objets émetteurs : géométrie des disques d’accrétion de pulsars, champ magnétique au cœur des restes de supernovæ ou encore détermination du spin des trous noirs. Ces informations fondamentales sont pour l’instant inaccessibles à cause de l’absence de polarimètres X performants.L’utilisation de l’effet photoélectrique pour effectuer de la mesure spectro polarimétrique des rayons X mous dans la bande d’énergie de 1 keV à 15 keV apparaît comme une approche bien plus adaptée que l’utilisation de la diffraction de Bragg ou de la diffusion Thomson. La polarimétrie par le truchement de l’effet photoélectrique repose sur la mesure de la direction d’éjection du photoélectron, laquelle est modulée par la direction de polarisation de la lumière incidente. Il s’agit alors de construire un détecteur permettant un recul suffisant des photoélectrons afin de reconstruire leurs traces, et les détecteurs gazeux sont par nature des candidats idéaux. Cette thèse traite du développement et de la caractérisation d’un spectro-polarimètre `a rayons X-mous d’un genre entièrement nouveau : Caliste-MM. Il consiste en un détecteur gazeux, le piggyback Micromegas associé à une électronique de lecture miniature baptisée Caliste. L’une des principales innovations de ce détecteur tient au fait que son électronique de lecture est située en dehors du milieu gazeux. Les charges créées dans le piggyback diffusent dans une couche résistive répandue sur une céramique venant fermer le détecteur gazeux. Le module électronique Caliste enregistre le signal qui se répand dans la couche résistive à travers la céramique et une fine lame d’air par couplage capacitif. Le détecteur est ainsi composé de deux parties complètement indépendantes : conversion de la lumière et amplification par le piggyback, et lecture du signal par le Caliste. Les deux peuvent alors être développées indépendamment l’une de l’autre, l’électronique étant protégée des étincelles développées dans le détecteur grâce à la couche résistive du piggyback.Les caractéristiques détaillées du détecteur sont étudiées et présentées : forme des évènements, gain, résolution en énergie, ainsi que la variation de ces caractéristiques avec les différents paramètres du détecteur. Des modèles analytiques sont comparés aux résultats obtenus afin d’expliciter les phénomènes physiques responsables de la topologie des évènements enregistrés. Les différentes méthodes pour obtenir une trace reconstructible issue de photoélectrons sont aussi étudiées : utilisation d’une électronique de lecture plus finement pixélisée (utilisant ainsi pleinement le concept d’électronique découplée), test en basse pression ou utilisation de gaz légers comme l’Hélium ou le Néon.Enfin, grâce à des mesures effectuées sur le faisceau 100% polarisé de la ligne Métrologie du synchrotron SOLEIL, le facteur de modulation du détecteur est mesuré et présenté à différentes énergies de 6 à 12 keV. Une mesure du facteur de modulation de 92% à 8 keV prouve le grand potentiel de ce nouveau spectro-polarimètre et l’intérêt de son concept innovant. / Performing X-ray polarimetry of astrophysical sources could provide precious insight into the properties of the emitting objects, for example the geometry of pulsars accretion disks, magnetic field inside the core of supernovae remnants or measurement of black holes spin. These fundamental observations are today impossible due to the missing performance of X-ray polarimeters. The use of the photo-electric effect to perform spectro-polarimetry in the energy band of 1 keV to 15 keV appears to be like a much better approach than the use of Bragg diffraction or Thomson scattering. Performing polarimetry with the photo-electric effect relies on the measurement of the ejection direction of the photo-electron, which is modulated by the polarization direction of the incoming light. In order to reconstruct the photo-electron track, a detector allowing the photo electrons to recoil far enough is needed. Gaseous detectors are naturally perfect candidates. This PhD thesis focusses on the development and the characterization of a soft X-ray spectro- polarimeter of a completely new design : Caliste-MM. It consists of a gaseous detector called piggyback Micromegas associated with a miniature 3D readout electronics baptized Caliste. The main innovation of this detector comes from the fact that its readout electronics is located outside the gaseous medium. The charges created inside the piggyback diffuse in a resistive layer spread on a solid ceramic plate that closes the detector. The Caliste records the signal of the charges in the resistive layer through the ceramic and a small air layer by capacitive induction. The detector is composed of two completely independent parts : the piggyback where the X-ray conversion and amplification takes place, and the Caliste for the recording of the signal. These two parts can then be developed independently. Moreover the electronics are protected from sparks thanks to the resistive layer of the piggyback.The detailed characteristics of the detector are studied such as the shape of the events, the gain and the energy resolution. Analytical models are compared to the obtained results in order to explain the physical phenomena responsible for the topology of the recorded events. Different strategies to improve the reconstruction of the photo-electrons are explored including for example finer pitched readout electronics, low pressure and the use of lighter gases such as Neon or Helium. Finally, thanks to the measurements performed on the 100% linearly polarized beam of the Mtrologie line of the SOLEIL synchrotron facility, the modulation factor of the detector has been measured at different energies ranging from 6 keV to 12 keV. A measurement of the modulation factor of 92% at 8 keV proves the high potential of this new spectro-polarimeter and the interest into its innovative design.

The graduation thesis is engaged in the design of computed tomography (CT). It is a piece of medical equipment which helps to define the diagnosis of a patient. The first part of the project is a research into contemporary stage and production of CT systems. Consequently the new design of computed tomography is designed in a way to maximise ergonomical, technical and aesthetic quality.