Dependency of energy-, position- and depth of interaction resolution on scintillation crystal coating and geometry

Options for optimizing the energy and spatial resolution of gamma-ray imaging detectors based on thick, monolithic crystals shaped like fiat-topped pyramids were studied. Monte Carlo simulations were made of the scintillation light transport for evaluating the effect of four parameters on the energy resolution, the spatial resolutions, and the depth of interaction (DOI) resolution of the gamma-ray imaging detector. These four parameters are: the reflectivity of the surface coating; the scatter mean free path; the absorption mean free path of the scintillation light; and the angle that defines the inclination of the sides of the pyramidal frustum. In real detectors, the values for the mean free paths for optical photons are normally not known. We estimated these by comparing MC simulations of detector resolutions to measurements for three gamma-ray imaging detectors with LYSO and LSO from different suppliers and with different surface coatings and geometries. The gamma-ray imaging detector measures the energy, centroids, and depth of interaction of the gamma-ray. DOI enhanced charge dividing readouts were used to measure the depth of interaction. Index Terms--Crystal geometry, gamma ray imaging, interaction depth, monolithic scintillator, surface coating.