Ionization-density-dependent Scintillation Pulse Shape and Mechanism of Luminescence Quenching in LaBr3:Ce

TL;DR

This paper models the ionization-density-dependent scintillation pulse shape in LaBr3:Ce, revealing nonlinear quenching of Ce3+ ions as the key to pulse-shape differences and extending findings to other scintillators.

Contribution

The study introduces a quantitative model explaining pulse-shape differences in LaBr3:Ce based on nonlinear quenching, and predicts similar effects in other fast scintillators.

Findings

Model reproduces electron and alpha particle responses.

Nonlinear quenching of Ce3+ ions causes pulse-shape differences.

Predictions confirmed in other scintillators like LYSO and CeBr3.

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. In this paper, 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 nonproportionality response of electrons or {\alpha} particles, and explains the measured {\alpha} and {\gamma} pulse-shape difference well. In particular, the nonlinear quenching of excited dopant ions, Ce3+, is confirmed herein to mainly contribute observable ionization {\alpha} and {\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 lutetium yttrium oxyorthosilicate, Lu2(1-x)Y2xSiO5:Ce (LYSO) and CeBr3, are also predicted and verified with experiments.