Characterization of Large Volume 3.5 x 8 inches LaBr3:Ce Detectors

TL;DR

This study thoroughly characterizes large volume 3.5 x 8 inches LaBr3:Ce scintillation detectors, analyzing their energy and time resolution, linearity, and efficiency for high-energy gamma-ray detection, with implications for their practical applications.

Contribution

It provides the first comprehensive characterization of these large LaBr3:Ce detectors, including effects of voltage dividers, crystal non-homogeneities, and PMT gain drifts.

Findings

High light yield leads to response deviations and pulse shape deformation.

Energy resolution affected by crystal non-homogeneities and PMT gain drifts.

Detectors achieve high efficiency up to 30 MeV gamma rays.

Abstract

The properties of large volume cylindrical 3.5 x 8 inches (89 mm x 203 mm) LaBr3:Ce scintillation detectors coupled to the Hamamatsu R10233-100SEL photo-multiplier tube were investigated. These crystals are among the largest ones ever produced and still need to be fully characterized to determine how these detectors can be utilized and in which applications. We tested the detectors using monochromatic gamma-ray sources and in-beam reactions producing gamma rays up to 22.6 MeV; we acquired PMT signal pulses and calculated detector energy resolution and response linearity as a function of gamma-ray energy. Two different voltage dividers were coupled to the Hamamatsu R10233-100SEL PMT: the Hamamatsu E1198-26, based on straightforward resistive network design, and the LABRVD, specifically designed for our large volume LaBr3:Ce scintillation detectors, which also includes active semiconductor devices. Because of the extremely high light yield of LaBr3:Ce crystals we observed that, depending on the choice of PMT, voltage divider and applied voltage, some significant deviation from the ideally proportional response of the detector and some pulse shape deformation appear. In addition, crystal non-homogeneities and PMT gain drifts affect the (measured) energy resolution especially in case of high-energy gamma rays. We also measured the time resolution of detectors with different sizes (from 1x1 inches up to 3.5x8 inches), correlating the results with both the intrinsic properties of PMTs and GEANT simulations of the scintillation light collection process. The detector absolute full energy efficiency was measured and simulated up to gamma-rays of 30 MeV