Alpha-event and surface characterisation in segmented true-coaxial HPGe detectors

TL;DR

This study investigates alpha interactions on the surface of true-coaxial high-purity germanium detectors, revealing a thinner-than-expected dead layer and discussing implications for background signals in neutrinoless double beta decay experiments.

Contribution

It provides detailed characterization of alpha events and surface properties in segmented HPGe detectors, highlighting potential background sources for rare event searches.

Findings

Alpha events indicate a dead layer less than 20 μm thick.

Surface contamination can mimic signals for neutrinoless double beta decay.

Guidance on preventing alpha-induced background signals.

Abstract

A detailed study of alpha interactions on the passivation layer on the end-plate of a true-coaxial high-purity germanium detector is presented. The observation of alpha events on such a surface indicates an unexpectedly thin so-called "dead layer" of less than 20 {\mu}m thickness. In addition, the influence of the metalisation close to the end-plate on the time evolution of the output pulses is discussed. The results indicate that alpha contamination can result in events which could be mistaken as signals for neutrinoless double beta decay and provide some guidance on how to prevent this.