Prompt Gamma Rays in 77Ge after Neutron Capture on 76Ge

The observation of neutrinoless double beta decay would be proof of the Majorana nature of the neutrino. Half-lives for these decays are very long (for Ge-76: > 10(25) y), so background reduction and rejection is the major task for double beta experiments. The GERDA (GERmanium Detector Array) experiment at the Gran Sasso Laboratory of the INFN (LNGS) searches for neutrinoless double beta decay of Ge-76. The isotope Ge-76 is an ideal candidate because it can be used as source and detector at the same time. A large remaining contribution to the background arises from the prompt gamma cascade after neutron capture by Ge-76 followed by beta(-)-decay of Ge-77. Since the prompt gamma decay scheme is poorly known, measurements with isotopically enriched Germanium samples were carried out at the PGAA facility at the research reactor FRM II (Munich). With the known prompt gamma spectrum it will be possible to improve the overall veto efficiency of the GERDA experiment.