published_or_final_version / abstract / Physics / Master / Master of Philosophy

The goal of this work reported here is to test the limits of the ECPSSR theory in the transition region of the low Z1/Z2.

No description available.

The cosmic X-ray background was discovered at the dawn of the X-ray astronomy: during the first successful rocket flight launched to study the X-ray emission from the Moon, the presence of a residual diffuse emission was also "serendipitously" revealed. In the intervening decades, observations with improving angular and spectral resolution have enhanced our understanding of the components that make up this background. Above 1 keV, the emission is highly isotropic on large angular scales, has extragalactic origin, and about ~80 percent has been resolved into discrete sources (Mushotzky et al. 2000, Hasinger et al. 1998). Our current interpretation of the diffuse X-ray emission below 1 keV uses a combination of 5 components, solar wind charge exchange, Local Bubble, Galactic halo, intergalactic gas, and unresolved point sources. Resolving the different components is made particularly difficult by the similar spectral emission of most components, X-ray lines of heavily ionized metals, which are poorly resolved by the energy resolution of CCD cameras onboard current X-ray satellites with typical observing times. The goal of this investigation is to assess the integral emission of the major components of the diffuse Soft X-Ray Background. In the first part of my project, I analyzed the shadow observations performed with XMM-Newton and Suzaku X-ray observatories. Shadow observations offer a tool to separate the fore ground component, due to the Local Bubble and, possibly, charge exchange within the solar system, from the background component, due primarily to the Galactic Halo and unidentified point sources. In the second part of my project, I studied the contribution of unresolved point sources and intergalactic medium to the diffuse Soft X-ray Background.

published_or_final_version / Physics / Master / Master of Philosophy

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.

Small-animal x-ray imaging is an important tool for medical research. The penetration power of x-rays makes it possible to investigate the 3D structure of small animals and other thick biological samples by computed tomography (CT). However, small-animal x-ray imaging often requires high resolution due to the small structures involved, and short exposure times due to sample movement. This constitutes a challenge, since these two properties require compact x-ray sources with parameters that are not widely available. In this Thesis we present the first application of liquid-metal-jet sources for small-animal imaging. This source concept was invented at KTH just over ten years ago. The use of a high-speed metal jet as electron-beam target, instead of a solid anode, enables higher x-ray flux while maintaining a small x-ray spot for high-resolution imaging. In the present work, a liquid-metal jet source with a higher-energy spectrum has been developed. It has stronger 24 keV radiation compared to previous sources, which makes it more suitable for imaging of small animals and other few-cm-thick objects, which require the higher penetration of 20-35 keV x-rays. We have applied the liquid-metal-jet x-ray sources for whole-body imaging of sacrificed mice and zebrafish. With high-resolution absorption-contrast CT we have visualized fine bone details of mice. We have also used phase contrast, a new method that can considerably improve imaging of, e.g., soft tissue, for demarcation of mm-sized tumors inside a full mouse and for mouse cartilage imaging. In zebrafish imaging, we have exploited the greatly enhanced contrast of phase-imaging to resolve single muscle fibers (and possibly even myofibrils) in whole zebrafish in a laboratory setting for the first time. The muscle structures have diameters in the 5-7 μm range and extremely low contrast, which makes them difficult to observe. With phase contrast, we have demonstrated low-dose and high-resolution angiography of mouse and rat organs and tissues ex vivo. We show detection of blood vessels with diameters below 10 μm with radiation doses compatible with living small animals, which is not possible with absorption contrast and iodinated contrast agents. In addition, we have investigated the vascular network of tumors in mouse ears and visualized the chaotic arrangement of newly-formed blood vessels. Finally, we present the first results from a new high-power liquid-metal-jet x-ray source prototype, operating at 10× the power of our previous sources, with the same x-ray spot size. This source constitutes an important step towards future in-vivo small-animal laboratory imaging with high resolution. / Röntgenavbildning av små försöksdjur är en viktig metod inom medicinsk forskning. Röntgenstrålar penetrerar material, vilket gör det möjligt att undersöka 3D-strukturen hos försöksdjur och andra tjocka biologiska prov med hjälp av datortomografi (CT). Tyvärr kräver smådjursavbildning ofta dels hög upplösning, eftersom de relevanta strukturerna är små, dels korta exponeringstider, eftersom objektet tenderar att röra sig. Detta är en utmaning, då båda egenskaperna kräver kompakta röntgenkällor med speciella egenskaper som inte är brett tillgängliga. I denna avhandling visar vi den första användningen av metallstråleröntgenkällor för avbildning av hela smådjur. Den här typen av röntgenkälla uppfanns vid KTH för drygt tio år sedan. Genom att låta elektronerna träffa en stråle av flytande metall, istället för en solid metallanod, kan vi generera mer röntgenstrålning men samtidigt behålla en liten källpunkt, vilket behövs för avbildning med hög upplösning. En ny metallstrålekälla utvecklades som en del av denna avhandling. Den ger ett röntgenspektrum med högre energier, vilket gör källan mer lämpad än tidigare källor för avbildning av små försöksdjur och andra centimetertjocka biologiska objekt. Vi har använt metallstrålekällor för att avbilda intakta, avlivade möss och zebrafiskar. Med högupplöst absorptions-CT har vi detekterat små bendetaljer inuti möss. Vi har även använt faskontrastavbildning, en ny metod som avsevärt kan förbättra avbildning av mjukvävnad, till att demarkera millimeterstora tumörer inuti en hel mus, samt för avbildning av brosk i leder hos möss. Faskontrast ger en kraftig förstärkning av kontrasten i bilden, vilket även har använts för att för första gången detektera individuella muskelfibrer (och eventuellt även myofibriller) inuti zebrafiskar med en kompakt röntgenkälla. Muskelstrukturerna har diametrar på 5-7 μm och låg kontrast, vilket gör dem svåra att observera. Med hjälp av faskontrast har vi utvecklat en metod för att avbilda blodkärl med diametrar under 10 μm inuti organ och vävnader från möss och råttor ex vivo, med stråldoser som är kompatibla med studier av levande smådjur. Detta är inte möjligt med konventionell absorptionskontrast och jod-baserade kontrastmedel. Vi har dessutom avbildat nyformade blodkärl kring tumörer i musöron och observerat kärlens kaotiska struktur. Slutligen presenterar vi de första resultaten från en prototyp av en ny högeffektskälla. Källan har tio gånger högre effekt än tidigare metallstrålekällor, men bibehåller samma storlek på källpunkten. Den här högeffektskällan är ett viktigt steg mot framtida laboratoriebaserad avbildning av levande små försöksdjur med hög upplösning. / <p>QC 20150331</p>

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.

Thesis (Ph. D.)--Michigan State University. Dept. of Astronomy and Astrophysics, 2008. / Title from PDF t.p. (viewed on July 23, 2009) Includes bibliographical references (p. 238-251). Also issued in print.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.