Made available in DSpace on 2014-10-09T12:53:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:12Z (GMT). No. of bitstreams: 0 / O objetivo do presente trabalho foi a avaliação do envelhecimento de um tubo de raios X com anodo de tungstênio utilizado para aplicações de radiodiagnóstico, por meio de aplicação de cargas de acordo com distribuições de cargas de trabalho da realidade brasileira e avaliações periódicas de grandezas associadas à qualidade de radiação produzida. Para o propósito deste trabalho, um sistema clínico com retificação monofásica de onda completa foi utilizado. Para avaliação em longo prazo das características do tubo de raios X relacionadas à carga de trabalho foi necessária a medição de parâmetros que pudessem representar de forma quantitativa o envelhecimento do tubo de raios X, estando estes relacionados principalmente ao desgaste do anodo. Esta medição indireta do envelhecimento do tubo levou a escolha de quatro parâmetros, alguns deles normalmente empregados na prática de controle de qualidade de equipamentos de radiologia diagnóstica: primeira e segunda camada semi-redutora (CSR), dimensões dos pontos focais, medida não invasiva do Potencial de Pico Prático e espectrometria de raios X. Estes parâmetros foram medidos inicialmente e após cada aplicação de carga pertinente. Para garantir a confiabilidade dos resultados, condições de reprodutibilidade foram estabelecidas para cada parâmetro de avaliação. As incertezas envolvidas em todos os processos de medição foram calculadas para avaliação da real contribuição dos efeitos do envelhecimento do tubo de raios X nos parâmetros não invasivos. Dentre os parâmetros avaliados, os que mostraram maior sensibilidade aos efeitos da aplicação de carga em longo prazo foram as energias médias obtidas por meio de espectrometria de raios X e as camadas semi-redutoras. Um modelo relacionado a estes parâmetros foi aplicado e estimativas da taxa de envelhecimento do tubo de raios X para diferentes tensões de aceleração e correntes anódicas foram obtidas. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

An increasing number of fields would benefit from a single analytical probe that can characterise bulk objects that vary in morphology and/or material composition. These fields include security screening, medicine and material science. In this study the X-ray region is shown to be an effective probe for the characterisation of materials. The most prominent analytical techniques that utilise X-radiation are reviewed. The study then focuses on methods of amalgamating the three dimensional power of kinetic depth X-ray (KDFX) imaging with the materials discrimination of angular dispersive X-ray diffraction (ADXRD), thus providing KDEX with a much needed material specific counterpart. A knowledge of the sample position is essential for the correct interpretation of diffraction signatures. Two different sensor geometries (i.e. circumferential and linear) that are able to collect end interpret multiple unknown material diffraction patterns and attribute them to their respective loci within an inspection volume are investigated. The circumferential and linear detector geometries are hypothesised, simulated and then tested in an experimental setting with the later demonstrating a greater ability at discerning between mixed diffraction patterns produced by differing materials. Factors known to confound the linear diffraction method such as sample thickness and radiation energy have been explored and quantified with a possible means of mitigation being identified (i.e. via increasing the sample to detector distance). A series of diffraction patterns (following the linear diffraction appoach) were obtained from a single phantom object that was simultaneously interrogated via KDEX imaging. Areas containing diffraction signatures matched from a threat library have been highlighted in the KDEX imagery via colour encoding and match index is inferred by intensity. This union is the first example of its kind and is called diffraction enhanced KDEX imagery. Finally an additional source of information obtained from object disparity is explored as an alternative means of calculating sample loci. This offers a greater level of integration between these two complimentary techniques as object disparity could be used to reinforce the results produced by the linear diffraction geometry.

Lynx is a concept under study for prioritization in the 2020 Astrophysics Decadal Survey. Providing orders of magnitude increase in sensitivity over Chandra, Lynx will examine the first black holes and their galaxies, map the large-scale structure and galactic halos, and shed new light on the environments of young stars and their planetary systems. In order to meet the Lynx science goals, the telescope consists of a high-angular resolution optical assembly complemented by an instrument suite that may include a High Definition X-ray Imager, X-ray Microcalorimeter and an X-ray Grating Spectrometer. The telescope is integrated onto the spacecraft to form a comprehensive observatory concept. Progress on the formulation of the Lynx telescope and observatory configuration is reported in this paper.

Metal halide perovskites (MHPs) have attracted the attention of researchers particularly in the photo-absorption field. These materials rival traditional semiconductors with their cost-effective ease of synthesis, tunable bandgaps, and excellent photophysical properties. Single-junction MHP solar cells have rivaled current silicon-based photovoltaic devices, boasting a 25.2% light absorption conversion. Recently, MHPs have proven to be effective in x-ray detection. In this paper an investigation of three titanium-based MHPs was conducted. The goal of this research was to characterize the MHPs and determine if they are feasible materials to incorporate in x-ray detectors. After completing the research, two MHP species, FA2TiI6 and MA3TiCl7, were able to be synthesized and characterized. Their crystal systems were determined to be tetragonal with a P4/mmm space group. However, due to equipment limitations, their feasibility in x-ray detectors could not be determined.

This thesis investigates the use of x-ray fluorescence (XRF) measurements of skin iron concentration as a non-invasive surrogate marker for total body iron burden. Rats were overloaded with iron dextran via intraperitoneal injection to investigate trends in iron accumulation in skin and organs. The skin, heart, liver, and kidney of the animals were collected and the iron concentrations were measured using the Huber XRF system and the polarized energy dispersive x-ray fluorescence (PEDXRF) system. When measured in the Huber XRF system, a very strong quadratic correlation was found between skin iron concentration and liver iron concentration (R2=0.92). In the same system, skin iron concentration had a moderately strong linear correlation with heart and kidney iron concentration (R2=0.53 and R2=0.65, respectively). Measured in the PEDXRF system, heart and kidney iron concentrations were again linearly correlated with skin iron concentrations (R2=0.34 and R2=0.31, respectively). Liver iron concentration again showed a quadratic correlation with skin iron concentration (R2=0.64). Therefore, it was demonstrated that skin iron concentrations can act as a surrogate marker for organ iron concentrations in rats, especially for the liver. The feasibility of using an Olympus Innov-X Delta Professional Handheld XRF Analyzer, a commercial portable x-ray fluorescence (PXRF) device, as a tool for in vivo skin iron analysis was investigated. The same rat skin samples measured in the previous experiment were measured using the PXRF device and compared with the organ iron concentrations as measured using the Huber XRF system. The heart and kidney showed linear correlations with skin iron concentration (R2=0.45 and R2=0.36, respectively). The liver showed the strongest correlation with a moderately strong quadratic correlation with R2=0.74. It was determined that using Beam 3 in the Soil mode of this device resulted in equivalent and effective dose rates of 230±10mSv/min and 2.3±0.1mSv/min, respectively. Thus, the PXRF device has shown promise as a potential tool for measuring in vivo skin iron levels. / Thesis / Master of Science (MSc)

Cadmium (Cd) is a highly toxic metallic element to the human body such that prolonged occupational or environmental exposure produces renal, hepatic, pneumonic, and neurological disorders. Thus, as a consequence it is important to have a way of monitoring cadmium exposure as it has the potential to become an occupational health hazard. The primary uses of this element are in the mining and smelting industry in the manufacture of cadmium alloys and the manufacture of alkaline accumulators. Since the discovery of X-rays in 1895 by Wilhelm Conrad Roentgen, the science of X-ray analysis has become a cardinal tool in all domains of chemical identification and classification. X-ray fluorescence (XRF) has been shown to be an effectual technique for measuring trace quantities of heavy metals such as lead in various tissues within the body. This thesis stud:r elucidates a means of measuring Cadmium in bone. The study assesses the feasibility and practicality of the polarised XRF and source excited techniques. In the polarised cadmium concentration measurements, a gain in sensitivity due to improved background characteristics was perused by increasing the x-ray tube operating voltage of the system. It was found that an operating voltage of 175 kV, and a copper filter resulted in a significant gain in sensitivity for which a minimum detection limit (MDL) of 3.5 ± 1.4 ppm was determined with 3 mm of tissue equivalent overlay. Using the source-based technique, a MDL of 3.5 ± 0.2 ppm was estimated for the corresponding tissue equivalent overlay. / Thesis / Master of Science (MS)

Call number: LD2668 .T4 1943 W3 / Master of Science

No description available.

X-ray Emission from Low Mass Binary Systems X-ray time-series and spectra of two LMXRBs are presented. The data are from the the well-known X-ray burster MXB1636-536 and the dipping source 4U1624-49. In the case of MXB1636-536, a simultaneous optical observation is also presented. The 2-20 keV persistent X-ray emission from MXB1636-536 is found to show both positive and negative hardness-flux correlations and to vary by a factor of &sim; 2 on timescales of hours. The persistent spectrum is best described by a power law with high energy cut-off, indicative that Comptonization dominates the spectral formation in the inner accretion disk. The temperature, optical depth and Compton y parameter of the Comptonizing plasma are derived; the Compton y parameter shows that the spectrum is consistent with unsaturated Comptonization. The negative hardness-flux correlation is explained in terms of the Compton cooling of a hot neutron star corona as a result of an increase in accretion rate. It is notable that a negative hardness-flux correlation and a power law spectrum is in direct conflict with previous observations of this source. Thirteen X-ray bursts, exhibiting a wide variety of profile, were also observed from MXB1636-536. The peak burst flux and burst fluence varied by a factor of 6 and 5 respectively. The burst sample may be divided into two distinct classes: those with fast rise and high peak intensity (strong) and those with slow rise and low peak intensity (weak). Moreover, the strong bursts are 'super-Eddington' and one of the weak bursts is unusual in that it is double-peaked in both the X-ray and bolometric burst profiles. The observed burst properties are discussed within the framework of the current thermonuclear flash models and other physical scenarios. One of the bursts, observed simultaneously in both the X-ray and optical wavebands, is used to determine the possible locality of the reprocessing region in the accretion disk. 4U1624-49 reveals a pattern of dips in the 1-10 keV X-ray light-curve which repeat with a period of ~21 hours. This is almost certainly the binary period of the system, making it one of the longest binary periods amongst LMXRBs. The &sim;25% residual flux can be associated with a physically extended emission component whereas the dips are associated with the intermittent obscuration of a compact component by material in the line-of-sight. The spectral changes occuring within the dips are complex and indicate energy-independent reductions in flux and substantial increases in absorption. The dips cannot be explained by a bulge at the outer disk edge (at the point of impact with the incoming stream) obscuring the central X-ray source. Assuming the primary of 4U1624-49 is a 1.4M? neutron star, the companion is likely to be an evolved star with a mass < 3M? and radius < 2.75R?. The orbital inclination is found to be within the range predicted by the FKL model for 'pure dippers' i.e. 60° < I < 75°.

The ROSAT Wide Field Camera (WFC) is an imaging experiment, conducted by a consortium of UK groups, intended to perform the first all sky survey in the XUV wavelength band (6-30nm). As part of the development and flight programmes, XUV calibration and background simulation work has been undertaken at Leicester. Here, the commissioning and development of an XUV line source and monochromator is described and their use to produce a laboratory detector standcird is reported. Subsequent efficiency calibration of a Csl coated prototype WFC MicroChannel plate detector is reported and the results shown to be in substantial agreement with a published model of photocathode behaviour. The results fill a gap in the published data between 11.2 and 25.6nm. Reflectivity measurements on the Wolter-Schwtirzschild Type 1 grazing incidence mirrors are reported and compared with the predictions of theory and with published measurements on test flats. Differences between theoretical reflectivities and the empirical results of up to 15% axe shown to be consistent with either: low density reflective gold coating, hydrocarbon contamination, or errors in the optical constants assumed for gold. Measurements were found to be broadly in agreement with published results. In addition to experimental work, the impact of the orbital low energy electron background is assessed on WFC performance and shown to be limiting due to the inclination of the spacecraft orbit. Reduction of this background is shown, by computer simulation, to be feasible by the introduction of a magnetic screen. Preliminary electron beam tests support this view.