Experimental and Computational Evaluation of Thickness-Dependent Reflection Coefficients of Scintillator-Photosensor Interfaces

Scintillator-photosensor interface reflection coefficient is a crucial parameter in estimating the absolute light yield (LY) of scintillators as it has an impact on the light transfer efficiency (LTE) of scintillating crystals [1], [2]. Typically, this parameter is assumed to be a single value for a given scintillator-photosensor coupling configuration, and LTE and LY calculations are carried out using this fixed value. However, the light reflection coefficient is known to be dependent on both the angle of incidence and the energy of photons, since the refractive index of a material is an energy-dependent quantity [3]. As the angular and energy distributions of light photons on the scintillator-photosensor interface change as a function of crystal thickness, we hypothesize that the interface reflection coefficient should also change as a function of crystal thickness. We provide Geant4 simulation results to support this hypothesis, and we show the method to estimate the interface reflection coefficient from the simulation results. We use a simplified analytical model to experimentally determine the scintillator-photosensor interface reflection coefficient. Finally, we use our experimental results for four LYSO crystals with different thicknesses [4] to validate the simplified model.