A new low-level γ-ray spectrometry system for environmental radioactivity at the underground laboratory Felsenkeller

A low-level gamma-ray spectrometry system, based on an HPGe-detector with 92% relative efficiency recently installed in the underground laboratory Felsenkeller at 110 m water equivalent (w.e.) depth, is described. The integral background count rate normalised to the Ge-crystal mass in the energy range from 40 keV until 2.7 MeV of 0.034 s(-1) kg(-1) has been achieved by careful material selection of the detector construction material, a graded shielding construction and effective radon suppression. The detector is highly suitable for the effective surveillance of water for human consumption with decision thresholds for Ra-226 and Ra-228 in the order of some mBq L-1. (c) 2009 Elsevier Ltd. All rights reserved.