Optimization of the HPGe detector passive shields by Monte-Carlo simulations

Abstract The selection of appropriate materials and their thicknesses, which should be used for germanium spectrometer shielding, is an important and complex task with the aim to reduce the contribution of background events to detector spectra. These background events have origin in the radioactive decay of environmental radionuclides, and also are produced by cosmic-ray muon induced secondary particles within shielding materials. In this work, the emission of gamma rays arising from members of U-238 and Th-232 series, as well as from K-40, distributed in the surroundings of the cylindrically-shaped shields was simulated, together with cosmic-ray muons of average energy 2 GeV, interacting with the shields. Different types of materials (Pb, Fe, Cu) including variations of the shield thickness were considered in simulations based on Geant4 software, while internal contamination of shielding material and radon buildup inside the shielding were not taken into account. The simulated spectra for germanium detector were analyzed and mutually compared. The results obtained were useful to provide optimal parameters for the shielding of germanium detectors against the external radiation — cosmic-ray muons and environmental gamma rays.