New developments for imaging energetic photons

Palmer, Max John (1997) New developments for imaging energetic photons. University of Southampton, Doctoral Thesis.

Abstract

The rapid evolution of synchrotron facilities able to produce highly intense, collimated beams of X-rays for scientific research poses a number of challenges for detector design. For example, there is a requirement for a position sensitive detector able to provide a 200 μ resolution over an area of 1000 cm² for use in protein crystallography. In this context, a novel integrating detector, able to meet the basic requirements of this 'imaging' application was evolved. This thesis explores the characteristics and quality of a projection-imaging technique intended to overcome the particular problem of high count rates associated with this application. A number of image reconstruction algorithms were evaluated, including filtered back-projection and a reconstruction algorithm based on the maximum entropy technique. Computer simulations demonstrated the clear advantages of the new, iterative, maximum entropy routine. Following this modelling activity, a prototype imaging system based upon the use of existing, silicon-strip detector technology was constructed, and good quality images obtained. Whilst an integrating detector of this type could indeed cope with very high photon fluxes, its ability to also meet the very large dynamic range requirements of the features in a diffraction pattern (10⁵) proved to be a serious limitation.

The technique of imaging by projection was also applied to be the design of a compact imager for environmental monitoring at 662 keV. This system was designed to the meet the need for a simple, imaging detector which is more compact than the present solutions. The development of a prototype, scanning detector is discussed and experimental images of both point-like and extended features, obtained at 662 keV, are presented. These results successfully demonstrate a practical implementation of the imaging technique and have suggested areas for improvements to be made to the detector design.

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