Monte Carlo simulations and investigation of the muon-induced background of the DLB

The Dortmund Low Background Facility (DLB) is a low-background gamma-ray spectrometry system built at ground level. It uses a high-purity germanium detector with a relative efficiency of 60 %, which is set up within an artificial overburden. This overburden consists of a massive outer shielding made of barite concrete and cast iron, corresponding to ten meters of water equivalent. It houses a multi-layer lead castle to shield against environmental radioactivities and uses borated polyethylene as a neutron absorber. Additionally, an active muon veto is installed to reduce the cosmic-induced muon contributions to the spectrum. The remarkably low background level of the DLB allows radio-purity screening measurements for material preselection and the detection of radionuclides with short half-lifes for activation analysis, with sensitivities well below the Bq/kg-level, which is comparable to laboratories located underground. In this talk the recently completed muon veto of the DLB is presented and estimations of the influence of the residual muonic contribution to the background spectrum using Monte Carlo simulations are given. These are most likely induced by the inefficiency of the used thin plastic scintillators. Therefore, most of them will be replaced by thicker plastic scintillators with a larger sensitive area.