Geant4-based technical simulation study of plastic scintillators for Positron Annihilation Lifetime Spectroscopy (PALS)

TL;DR

This study uses Geant4 simulations to analyze how the shape and size of ultra-fast plastic scintillators affect detection efficiency and spectrum quality in Positron Annihilation Lifetime Spectroscopy, highlighting design improvements.

Contribution

It provides a quantitative assessment of how scintillator geometry influences detection efficiency and IRF in PALS, which was previously understood mainly through empirical methods.

Findings

Truncated cone scintillators improve IRF precision.

Shape and size significantly affect detection efficiency.

Cylindrical shapes increase corrupt event rates.

Abstract

The influence of detector setup configuration and scintillator material choice on spectrum quality in Positron Annihilation Lifetime Spectroscopy (PALS) is fundamentally acknowledged primarily by empirical observation. However, this study quantifies the effects of ultra-fast plastic scintillators (BC422Q) within a conventional collinear (180-degree) detector setup used in the laboratory using the Geant4 simulation toolkit. We examine the impact of the scintillator's dimension and geometry (truncated cone vs. cylinder) on the detection efficiency for specific gamma-ray energies (1274 keV and 511 keV) and their proportion of corrupt events such as backscattering or multiple detections. Results indicate that the selection of scintillator dimension and shape significantly enhances detection efficiency albeit with an increase in corrupt events. Furthermore, we investigate the influence on the instrument response function (IRF) of the scintillators, showing how truncated cones offer superior precision and, thus, a narrower IRF compared to cylindrical shapes.