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

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 $\hat{I}\pm$-particles from the intrinsic Uranium and Thorium contamination in the scintillator. The ${\hat{I}}^2$-$\hat{I}\pm$ and the $\hat{I}\pm$-$\hat{I}\pm$ cascade decays from the U/Th decay chains were used to select $\hat{I}\pm$-particles. The contamination levels of U/Th were consequently measured to be $(5.54\pm 0.15)\times 10^{-11}$ g/g, $(1.45\pm 0.01)\times 10^{-10}$ g/g and $(1.07\pm 0.01)\times 10^{-11}$ g/g for ${}^{232}$Th, ${}^{238}$U and ${}^{235}$U, respectively, assuming secular equilibrium. The stopping power of $\hat{I}\pm$-particles in the liquid scintillator was simulated by the TRIM software. Then the Birks constant, $kB$, of the scintillator for $\hat{I}\pm$-particles was determined to be $(7.28\pm 0.23)$ mg/(cm${}^2\cdot$MeV) by Birks' formulation. The response for protons is also presented assuming the $kB$ constant is the same as for $\hat{I}\pm$-particles.

12 pages, 10 figures, 3 tables, prepared for submission to JINST