Investigating the anisotropic scintillation response in anthracene through neutron, gamma-ray, and muon measurements

TL;DR

This study characterizes the directional dependence of anthracene's scintillation response to neutrons, gamma rays, and muons, revealing anisotropy only in neutron-induced events and suggesting high dE/dx is necessary for anisotropy.

Contribution

It provides the first measurements of cosmic muon response and clarifies the conditions under which scintillation anisotropy occurs in anthracene.

Findings

Neutron-induced scintillation shows directional dependence.

Gamma-ray and muon responses show no significant anisotropy.

High dE/dx is necessary for scintillation anisotropy.

Abstract

This paper reports a series of measurements that characterize the directional dependence of the scintillation response of crystalline anthracene to incident DT neutrons, DD neutrons, Cs-137 gamma rays, and, for the first time, cosmic ray muons. The neutron measurements give the amplitude and pulse shape dependence on the proton recoil direction over one hemisphere of the crystal, confirming and extending previous results in the literature. In similar measurements using incident gamma rays, no directional effect is evident, and any anisotropy with respect to the electron recoil direction is constrained to have a magnitude of less than a tenth of that present in the proton recoil events. Cosmic muons are measured at two directions, and no anisotropy is observed. This set of observations indicates that high dE/dx is necessary for an anisotropy to be present for a given type of scintillation event, which in turn could be used to discriminate among different hypotheses for the underlying causes of the anisotropy, which are not well understood.