PNNL

Abstract

To probe the nature of the physical processes responsible for the nonlinear photon response of inorganic scintillators, we have combined a Monte Carlo (MC) code for calculating the microscopic spatial distributions of electron-hole pairs with a kinetic Monte Carlo (KMC) model of energy-transfer processes. In this publication, we focus on evaluating the contribution of an annihilation mechanism between self-trapped excitons (STE) to the photon response of pure CsI and Ce-doped LaBr3. A KMC model of scintillation mechanisms in pure CsI was developed previously and we introduce in this publication a similar model for Ce-doped LaBr3. We show that the KMC scintillation model is able to reproduce both the kinetics and efficiency of the scintillation process in Ce-doped LaBr3. Relative light output curves were generated at several temperatures for both scintillators from simulations carried out at 2, 5, 10, 20, 100, and 400 keV. These simulations suggest that STE-STE annihilation can account for the initial rise in relative light yield with increasing incident energy. This is due to the fact that the proportion of high-density regions decreases as the incident energy increases thus reducing the likelihood for STE-STE encounter. In addition, the simulations clearly show a lack of temperature dependence of the relative light output, in agreement with a majority of experimental work on the temperature dependence of nonlinearity in inorganic scintillators.