Response of gadolinium doped liquid scintillator to charged particles: measurement based on intrinsic U/Th contamination

TL;DR

This study measures the response of gadolinium-doped liquid scintillator to charged particles using intrinsic U/Th contamination, determining contamination levels, stopping power, and Birks constant for alpha particles, relevant for neutron detection.

Contribution

First in-situ measurement of Gd-doped liquid scintillator response to charged particles using intrinsic U/Th decay chains, including contamination levels and scintillation quenching parameters.

Findings

U/Th contamination levels precisely measured.

Birks constant for alpha particles determined.

Response for protons also characterized.

Abstract

A measurement is reported for the response to charged particles of a liquid scintillator named EJ-335 doped with 0.5% gadolinium by weight. This liquid scintillator was used as the detection medium in a neutron detector. The measurement is based on the in-situ $\alpha$-particles from the intrinsic Uranium and Thorium contamination in the scintillator. The $\beta$-$\alpha$ and the $\alpha$-$\alpha$ cascade decays from the U/Th decay chains were used to select $\alpha$-particles. The contamination levels of U/Th were consequently measured to be $(5.54\pm0.15)\times 10^{-11}$ g/g, $(1.45\pm0.01)\times 10^{-10}$ g/g and $(1.07\pm0.01)\times 10^{-11}$ g/g for $^{232}$Th, $^{238}$U and $^{235}$U, respectively, assuming secular equilibrium. The stopping power of $\alpha$-particles in the liquid scintillator was simulated by the TRIM software. Then the Birks constant, $kB$, of the scintillator for $\alpha$-particles was determined to be $(7.28\pm0.23)$ mg/(cm$^{2}\cdot$MeV) by Birks' formulation. The response for protons is also presented assuming the $kB$ constant is the same as for $\alpha$-particles.