Simulation and verification of the cosmogenic background at the shallow depth GIOVE detector

Abstract

The GIOVE (Germanium Inner Outer VEto) detector setup is a low level Germanium spectrometer for material screening with elaborated shield located at the shallow depth underground laboratory of the Max-Planck-Institut für Kernphysik in Heidelberg. It is equipped with a double active muon veto with a total muon rejection efficiency of ~99% and there are also passive layers to moderate and capture neutrons. With this setup an integral count rate is achieved comparable to detectors far deeper underground. The detector and shield geometry has been implemented into a Monte Carlo simulation, using the simulation framework MaGe based on Geant4. The Monte Carlo simulation is employed to determine sample efficiencies for γ ray screening measurements as well as to reproduce the remaining detector background from cosmic ray muon-induced secondaries. In terms of the background modeling of the unvetoed γ ray spectrum an excellent agreement better than 10% in the integral count rate in (40, 2700) keV as well as for the 511 keV line has been found. However, concerning the expected number of neutrons at the diode, the simulation outcome lays 40-80% below the measurement results. Being able to reproduce the detector background in the simulation, the simulation can be used to further optimize the shield design.