Enhanced X-ray material classification using SiPMs and fast scintillators

闪烁晶体的图像分辨率通常由探测器正面的物理尺寸定义。这是由于晶体内闪烁的各向同性导致不能更准确地确定穿过探测器表面的辐射相互作用的位置。第一次使用伽马相机是在20世纪50年代，S发明了一种方法，将多个光电倍增管连接到一个探测器上，以实现更高水平的图像分辨率。该技术采用单次闪烁，并测量每个光电倍增管中同时检测的程度。在所有有源光电倍增管中测量的信号比率将取决于它们在晶体表面周围的位置和入射辐射在晶体内相互作用的位置。用于传输或CT成像的晶体通常在正面有许多毫米宽。晶体的尺寸限制了图像数据的固有网格分辨率。在成本驱动探测器设计的应用中，没有方法能够识别入射X射线在探测器晶体正面上的相互作用点，从而限制了晶体的节距和从晶体读出的光电倍增管的保真度。该PHD计划旨在通过开发一种使用闪烁体亚表面激光蚀刻(SSLE)来聚焦闪烁光分布的新技术，来逐步改变诸如在安全和医疗应用中使用的X射线成像设备的分辨率能力。SSLE技术，通常见于玻璃照片蚀刻，提供了一种方法，将原本各向同性的光学光分布限制在一个反映晶体内X射线相互作用点的位置。PHD研究将涉及使用Geant4或等效物对光学分段探测器组件内的X射线和光学信号进行理论模拟。他们将研究SSLE产生的光学边界的最佳性质，以及所需的物理细节，如间距和边界位置对图像分辨率的影响。这些数据将被用来影响SSLE轮廓，以优化信号分割，然后使用X射线源来表征最终的SSLE晶体。这项研究可能会影响用于X射线成像的闪烁体探测器的设计，例如用于医学成像或安全筛查的闪烁体探测器，但也可以提高核工业用来探测特殊核材料中的伽马射线和中子的探测器的位置分辨率，因此在应用物理领域具有广泛影响的潜力。

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.