Ionization-density-dependent Scintillation Pulse Shape and Mechanism of Luminescence Quenching in LaBr 3 :Ce

Abstract

Pulse shape discrimination (PSD) is usually achieved using the different fast and slow decay components of inorganic scintillators, such as BaF2, CsI:Tl, etc. However, LaBr3:Ce is considered to not possess different components at room temperature, but has been proved to have the capability of discriminating gamma and alpha events using fast digitizers. The physical mechanism of such PSD capability of single-decay component LaBr3:Ce was still unclear. Ionization density-dependent transport and rate equations are used to quantitatively model the competing processes in a particle track. With one parameter set, the model reproduces the non-proportionality response of electrons or alpha particles, and predicts the measured {\alpha}/{\gamma} pulse shape difference. In particular, the nonlinear quenching of excited dopant ions, Ce3+, is confirmed herein for the first time to mainly contribute observable ionization {\alpha}/{\gamma} pulse shape differences. Further study of the luminescence quenching can also help to better understand the fundamental physics of nonlinear quenching and thus improve the crystal engineering. Moreover, based on the mechanism of dopant quenching, the ionization density-dependent pulse shape differences in other fast single-decay-component inorganic scintillators, such as LYSO and CeBr3, are also predicted and verified with experiments.