Monte-Carlo calculation of production rates of cosmogenic radionuclides in a HPGe detector operating in the Modane underground laboratory

Abstract

Monte Carlo models based on GEANT4, CONUS and ACTIVIA software packages were used for simulation of production rates of cosmogenic radionuclides in the Obelix HPGe detector operating in the Modane underground laboratory. Interactions of secondary cosmic-ray nucleons with Ge-crystal (production of 3H, 54Mn, 57CO, 65Zn and 68Ge), with copper in the cold finger (production of 46Sc, 54Mn, 56Co, 57Co, 58Co, 60Co and 59Fe), with Al in bauxite ore (production of 26Al) and with Al-4%Si alloy in the cryostat (production of 22Na) were included in the calculations. The contribution of cosmogenic radionuclides to the total detector background of the Obelix detector decreased from 39% (after 10 months of cooling down) to 14% (after three years of cooling down). The calculated production rates of cosmogenic radionuclides and simulated gamma-ray spectra were in reasonable agreement with experimental results.