Characterization of a broad energy germanium detector and application to neutrinoless double beta decay search in Ge-76

TL;DR

This paper thoroughly characterizes a broad energy germanium detector, focusing on its performance and response, and demonstrates its suitability for neutrinoless double beta decay searches in Ge-76.

Contribution

It provides detailed measurements of detector performance and investigates unique charge collection behaviors, enhancing understanding for neutrinoless double beta decay experiments.

Findings

Excellent energy resolution and stability achieved.

Identified peculiar charge collection behavior around 2000V bias.

Effective event discrimination using pulse shape analysis.

Abstract

The performance of a 630g commercial broad energy germanium (BEGe) detector has been systematically investigated. Energy resolution, linearity, stability vs. high-voltage (HV) bias, thickness and uniformity of dead layers have been measured and found to be excellent. Special attention has been dedicated to the study of the detector response as a function of bias HV. The nominal depletion voltage being 3000V, the detector under investigation shows a peculiar behavior for biases around 2000V: in a narrow range of about 100V the charge collection is strongly reduced. The detector seems to be composed by two parts: a small volume around the HV contact where charges are efficiently collected as at higher voltage, and a large volume where charges are poorly collected. A qualitative explanation of this behavior is presented. An event-by-event pulse shape analysis based on A/E (maximum amplitude of the current pulse over the total energy released in the detector) has been applied to events in different energy regions and found very effective in rejecting non localized events. In conclusion, BEGe detectors are excellent candidates for the second phase of GERDA, an experiment devoted to neutrinoless double beta decay of Ge-76.