Monte Carlo studies and optimization for the calibration system of the GERDA experiment

The GERmanium Detector Array, GERDA, searches for neutrinoless double is decay in Ge-76 using bare highpurity germanium detectors submerged in liquid argon. For the calibration of these detectors 7 emitting sources have to be lowered from their parking position on the top of the cryostat over more than 5 m clown to the germanium crystals. With the help of Monte Carlo simulations, the relevant parameters of the calibration system were determined. It was found that three Th-228 sources with an activity of 20 kBq each at two different vertical positions will be necessary to reach sufficient statistics in all detectors in less than 4 h of calibration time. These sources will contribute to the background of the experiment with a total of (1.07 +/- 0.04(stat) (+0.13)(-0.19)(sys)) is 10(-4) ctsAkeV kg yr)) when shielded from below with 6 cm of tantalum in the parking position. (C) 2013 Elsevier B.V. All rights reserved.