The upgraded low-background germanium counting facility Gator for high-sensitivity $\gamma$-ray spectrometry

TL;DR

The paper details the upgrade and performance of the Gator germanium detector, enhancing its low-background gamma-ray spectrometry capabilities for material screening in rare-event physics experiments.

Contribution

It presents a significant upgrade to the Gator facility, reducing background rates and demonstrating improved sensitivity for ultra-low background measurements.

Findings

Background rate reduced by 20% after upgrade

Gator's stability over time is confirmed

Demonstrated sensitivity with a DARWIN candidate sample

Abstract

We describe the upgrade and performance of the high-purity germanium counting facility Gator, which is dedicated to low-background $\gamma$-ray spectrometry. Gator is operated at the Gran Sasso Underground Laboratory in Italy, at an average depth of 3600 meter water equivalent, and employed for material screening and selection in ultra-low background, rare-event search experiments in astroparticle physics. The detector is equipped with a passive shield made of layers of copper, lead and polyethylene, and the sample cavity is purged with gaseous nitrogen maintained at positive pressure for radon suppression. After upgrading its enclosure, the background rate is (82.0$\pm$0.7) counts/(kg$\cdot$day) in the energy region 100 keV to 2700 keV, a 20% reduction compared to the previously reported rate. We show the stability of various operation parameters as a function of time. We also summarize the sample analysis procedure, and demonstrate Gator's sensitivity by examining one material sample, a candidate photosensor for the DARWIN experiment.