Enhanced X-ray material classification using SiPMs and fast scintillators

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Image resolution from scintillating crystals is typically defined by the physical dimensions of the front face of the detector. This results from the inability to determine more accurately the location of the radiation interaction across the face of the detector due to the isotropic nature of the scintillation within the crystal. The first use of gamma cameras in the 1950's developed a method for using multiple photomultipliers attached to a single detector to achieve higher levels of image resolution. The technique takes the single scintillation and measures the degree of simultaneous detection in each of the photomultipliers. The ratio of signals measured in all of the active photomultipliers will depend both on their location around the crystal surface and the location of interaction of the incident radiation within the crystal.Crystals used in transmission or CT imaging are typically many mm across at the front face. The dimensions of the crystal limit the intrinsic grid-resolution of image data. There is no method for being able to identify the interaction point of the incident X-ray on the front face of the detector crystal in applications where cost drives the detector design, limiting the pitch of crystal and the fidelity of the photomultiplier readout from the crystal.This PhD program aims to make a step change in resolution capabilities of X-ray imaging equipment, such as employed in security and medical applications, by developing a novel technique for focusing the distribution of scintillation light with the use of scintillator sub-surface laser etching (SSLE). SSLE techniques, typically seen in glass photograph etching, provides a means for confining the otherwise isotropic distribution of optical light into a location that reflects the point of X-ray interaction within the crystal. The PhD study will involve the theoretical simulation of X-ray and optical signals within the optically segmented detector assembly, using Geant4 or equivalent. They will investigate the optimal properties of the optical boundaries created by SSLE and the required physical details such as pitch and boundary location on image resolution. The data will be used to influence the SSLE profile to optimize signal segmentation before characterising the final SSLE crystal using X-ray sources. This research could impact on scintillator detector design for X-ray imaging such as that used in medical imaging or security screening but also improve the position resolution of detectors that can used by nuclear industry to detect gamma-rays and neutrons from special nuclear materials and so has the potential for broad impact in areas of applied physics.