Gamma background studies in 45 m and 150 m deep mines

A very low background level is a key requirement for low-energy nuclear astrophysics experiments. A detailed high energy (E_gamma > 3 MeV) gamma-background study with two escape-suppressed HPGe detectors has been performed at a medium deep underground site, in the Reiche Zeche mine (150 m) in Freiberg, Germany [1]. The new data complement a data set with the same detector at the Earth's surface, shallow underground (45 m) in the Felsenkeller laboratory in Dresden, Germany [2], and deep underground (1400 m) in LNGS in Gran Sasso, Italy [3]. The detailed background data from one and the same escape-suppressed HPGe detector at different underground depths allows the investigation of the effect of the active and passive shielding on the high energy (E_gamma > 3 MeV) laboratory background. A detailed interpretation of the behaviour of different background components as a function of the underground depth will be presented. The data show that already a shallow underground site has sufficiently low gamma-background for many nuclear astrophysics studies when an additional active shield is used to veto the remaining muon flux. Benefiting from these low background conditions, a used 5MV Pelletron tandem accelerator is currently being refurbished for installation at the Dresden Felsenkeller [4].
[1] T. Szücs et al., Eur. Phys. J. A 51, 33 (2015).
[2] T. Szücs et al., Eur. Phys. J. A 48, 8 (2012).
[3] T. Szücs et al., Eur. Phys. J. A 44, 513 (2010).
[4] D. Bemmerer et al., Proc. of Sciences NIC XIII, 044 (2015).