Characterization of a GAGG detector for neutron measurements in underground laboratories

Abstract

In rare events experiments, such as those devoted to the direct search of dark matter, a precise knowledge of the environmental gamma and neutron backgrounds is crucial for reaching the design experiment sensitivity. The neutron component is often poorly known due to the lack of a scalable detector technology for the precise measurement of low-flux neutron spectra. Gd$_3$Al$_2$Ga$_3$O$_{12}$ (GAGG) is a newly developed, high-density scintillating crystal with a high gadolinium content, which could allow to exploit the high $(n,\gamma)$ cross section of $^{155}$Gd and $^{157}$Gd for neutron measurements in underground environments. GAGG crystals feature a high scintillation light yield, good timing performance, and the capability of particle identification via pulse-shape discrimination. In a low-background environment, the distinctive signature produced by neutron capture on gadolinium, namely a $\beta/\gamma$ cascade releasing up to 9 MeV of total energy, and the efficient particle identification provided by GAGG could yield a background-free neutron capture signal. In this work, we present the characterization of a first GAGG detector prototype in terms of particle discrimination performance, intrinsic radioactive contamination, and neutron response.