The GeMSE Facility for Low-Background {\gamma}-Ray Spectrometry

TL;DR

The paper presents the design, capabilities, and initial results of the GeMSE facility, a low-background germanium detector for sensitive gamma-ray spectrometry in astroparticle physics and meteorite analysis.

Contribution

It introduces a new high-purity germanium detector setup with advanced shielding and muon veto, achieving competitive background rates and sensitivity for rare isotope detection.

Findings

Achieved background rate of 246 counts/day in the 100-2700 keV range.

Measured sensitivity of approximately 0.5-0.6 mBq/kg for long-lived isotopes.

Extrapolated potential sensitivity in the 50 μBq/kg range for larger samples and longer measurements.

Abstract

We describe a new high-purity germanium (HPGe) detector setup for low-background {\gamma}-ray spectrometry. The GeMSE facility (Germanium Material and meteorite Screening Experiment) is dedicated to material screening for rare event searches in astroparticle physics as well as to the characterization of meteorites. It is installed in a medium depth (~620 m.w.e.) underground laboratory in Switzerland in a multi-layer shielding and is equipped with an active muon veto. We have reached a very competitive integral background rate of (246$\pm$2) counts/day (100-2700 keV) and measured a sensitivity of $\sim$0.5-0.6 mBq/kg for long-lived isotopes from the $^{238}$U/$^{232}$Th chains in a $\sim$1\,kg sample screened for $\sim$27 days. An extrapolation to higher sample masses and measurement times suggests a maximum sensitivity in the $\mathcal{O}(50)$ \mu Bq/kg range. We describe the data analysis based on Bayesian statistics, background simulations, the efficiency calibration and first sample measurements.