Long-Term Stability of Underground Operated CZT Detectors Based on the Analysis of Intrinsic ${}^{113}$Cd β${}^{-}$-Decay

Abstract

The COBRA collaboration operates a demonstrator setup at the underground facility LNGS (Laboratori Nazionali del Gran Sasso, located in Italy) to prove the technological capabilities of this concept for the search for neutrinoless double beta-decay. The setup consists of 64 $(1\times 1\times 1)$ cm${}^3$ CZT detectors in CPG configuration. One purpose of this demonstrator is to test if reliable long-term operation of CZT-CPG detectors in such a setup is possible. The demonstrator has been operated under ultra low-background conditions since more than three years and collected data corresponding to an exposure of 218 kg$\cdot$days. The presented study focuses on the long-term stability of CZT detectors by analyzing the intrinsic, fourfold forbidden non-unique ${}^{113}$Cd single beta-decay. It can be shown that CZT detectors can be operated stably for long periods of time and that the ${}^{113}$Cd single beta-decay can be used as an internal monitor of the detector performance during the runtime of the experiment.