GeMSE: a Low-Background Facility for Gamma-Spectrometry at Moderate Rock Overburden

Abstract

The GeMSE (Germanium Material and meteorite Screening Experiment) facility operates a low-background HPGe crystal in an underground laboratory with a moderate rock overburden of 620m.w.e. in Switzerland. It has been optimized for continuous remote operation. A multi-layer passive shielding, a muon veto, and a boil-off nitrogen purge line inside the measurement cavity minimize the instrument's background rate, which decreased by 33% to (164$\pm$2)counts/day (100-2700keV) after five years of underground operation. This agrees with the prediction based on the expected decay of short-lived isotopes. A fit to the known background components, modeled via a precise simulation of the detector, shows that the GeMSE background is now muon-dominated. We also present updates towards a more accurate detection efficiency calculation for the screened samples: the thickness of the crystal's outer dead-layer is precisely determined and the efficiency can now be easily calculated for any sample geometry. The advantage of this feature is showcased via the determination of the ${}^{40}$K content in the screening of a complex-shaped object: a banana.

References in corpus (3)

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• Cosmogenic activation of materials
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• A new ultra low-level HPGe activity counting setup in the Felsenkeller shallow-underground laboratory
• The upgraded low-background germanium counting facility Gator for high-sensitivity $\gamma$-ray spectrometry
• PANCAKE: a large-diameter cryogenic test platform with a flat floor for next generation multi-tonne liquid xenon detectors
• Development of a low-background HPGe detector at Kamioka Observatory