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About GeMSE's new Background ... and a banana

A new paper describes the current background level of the group's GeMSE low-background spectrometer, the (almost) fully remote operation of the facility and a novel way to simulate the detection efficiency of complex-shaped (e.g., banana-like) objects.
About GeMSE's new Background ... and a banana

Simulation of a banana in GeMSE

GeMSE is a low-background screening facility operated by the Freiburg Astroparticle Physics group. It is located at shallow depth of 620 m.w.e. in the Vue-des-Alpes laboratory in Switzerland, which is operated by AEC/LHEP at the University of Bern. The facility is used to measure the intrinsic radioactivity of materials and components to be used in rare event search experiments and of meteorites.

The core of the facility is a 2 kg HPGe crystal (mass: 2 kg) installed in a sophisticated shield. After five years of contiuous underground operation, several longer lived isotopes - initially produced by activation processes involving cosmic rays - have decayed away. This led to a 33% reduction of GeMSE's background rate, which is now only 82 events/(kg d) in the 100-2700 keV region.

In addition, the article presents the steps undertaken to allow for the full remote operation of GeMSE from Freiburg. At this point, the facility only needs to be visited to exchange samples or the bring liquid nitrogen (required for cooling) to the laboratory.

An important ingredient to correctly determine the radiactive contamination of a sample is the detection efficiency which is obtained from detailed Monte Carlo simulation of the sample-detector geometry. The article describes an innovative methods which allows the import of complex, irregular shapes, e.g., of meteorites or a banana, from 3d scans to the simulation program. The method is demonstrated on a banana; its measured 40K activity is 42.6 Bq, which agrees well with the usually adoped value for a standard banana.

  • Article:
    D. Ramirez Garcia, D. Baur, J. Grigat, B.A. Hofmann, S. Lindemann, D. Masson, M. Schumann, M. von Sivers, F. Toschi
    GeMSE: a Low-Background Facility for Gamma-Spectrometry at Moderate Rock Overburden
    JINST 17, P04005 (2022), arXiv:2202.06540