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Hall, David
(2010).
DOI: https://doi.org/10.21954/ou.ro.0000d730
Abstract
This thesis is concerned with exploring the way in which the physics of the detection process affects the quality of a CCD-based X-ray detector system. The physical processes which lead to the final images and spectra achieved with a CCD-based camera system are investigated through a combination of simulations and experimental techniques with the aim of improving the detector performance and allowing future detectors to be designed with optimal characteristics. Techniques developed throughout the study and the results of the simulations have wide-ranging impacts on the areas concerned. The study is split into two main sections, the first regarding a high-resolution, high-energy, photon-counting X/γ-ray camera. In medical imaging, X-rays and gamma-rays are often used for the purposes of diagnostic imaging. In many synchrotron based research programmes, such as protein crystallography and X-ray diffraction imaging, X-rays are used, once again, for imaging purposes. In both cases, a high-resolution detector with a high frame-rate is required such that images can be taken with a spatial resolution of the order of micrometers to tens of micrometers. If one is able to distinguish the energy of the incident X-rays and gamma-rays (with energies of 20-200 keV) then these spectral capabilities add to the functionality of the detector, allowing, for example, the removal of fluorescence X-rays. Chapter 2 reviews the relevant detector physics and theory before providing a critical review of current gammacameras. Chapter 3 outlines the feasibility study for the scintillator-coupled EM-CCD detailing the development of a new energy discrimination methodology. Also described is the development of a full system simulation which can be used to troubleshoot problems found when calibrating and optimising the device. Chapter 4 details the characterisation and optimisation of the detector making use of the aforementioned simulations where appropriate. Chapter 5 presents the results of the study, showing how the resolution can be dramatically improved and how energy discrimination can be implemented. The second section of the thesis regards instrument background. The use of CCDs for space borne X-ray detection in scientific satellites is wide-spread. Whilst in-orbit the CCDs are subjected to an incident flux of high energy particles. These particles may be detected, both as the primaries themselves and by means of secondaries produced in the detector shielding, and will produce a background level formed by components indistinguishable from the X-rays for which the mission was designed to detect. Chapter 6 presents an introduction to the theory behind the instrument background experienced by CCD-based detector systems in orbit. A simulation has been developed which is in very good agreement with data received from the spacecrafts, described in Chapter 7. Finally, Chapter 8 summarises the outcomes of these studies and provides insight into future work which will further aid the improvement of gamma-cameras for medical imaging and synchrotron-based research and will allow future CCD-based camera systems to be designed for increased sensitivity in-orbit.
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