Electron and Gamma Background in CRESST Detectors

TL;DR

This paper analyzes the background spectra in CRESST CaWO4 detectors, identifying sources like radioisotopes and cosmogenic activation, crucial for background reduction and detector calibration.

Contribution

It provides a detailed analysis of background sources in CRESST detectors, including detection of a specific 41-Ca decay line, aiding future background mitigation.

Findings

Identification of intrinsic and cosmogenic background sources

Detection of 41-Ca decay line with quantified activity

Cross-checking of detector calibration through background spectra

Abstract

The CRESST experiment monitors 300g CaWO_4 crystals as targets for particle interactions in an ultra low background environment. In this paper, we analyze the background spectra that are recorded by three detectors over many weeks of data taking. Understanding these spectra is mandatory if one wants to further reduce the background level, and allows us to cross-check the calibration of the detectors. We identify a variety of sources, such as intrinsic contaminations due to primordial radioisotopes and cosmogenic activation of the target material. In particular, we detect a 3.6keV X-ray line from the decay of 41-Ca with an activity of (26\pm4)\mu Bq, corresponding to a ratio 41-Ca/40-Ca=(2.2\pm0.3)\times10^{-16}.