Neutron-physical studies of germanium for experiments on neutrino double beta decay of 76Ge

One goal of modern physics is the experimental observation of the neutrinoless double beta decay (0νββ). Among the few naturally occurring nuclides 76Ge is one candidate to which this process is to verify, amongst others with the GERDA experiment. The extremely low probability of occurrence for a 0νββ-decay is of at least ten orders of magnitude smaller than that of the β--decay of 115In, one of the rarest beta transitions observed in nature with a half-life of 4.41 . 1014 years. Therefore a high detection sensitivity is required, which depends among other things on the measuring background. Its exact knowledge is necessary for the evaluation of the measuring data. In this work neutron-physical studies were performed on germanium aiming to close the essential gaps in this state of knowledge. Neutrons can cause counting events by direct interaction with germanium and the surrounding matter of the detector or indirectly by activation of any of these materials. For understanding of those background signals, the neutron interaction cross section 70Ge(n,3n)68Ge, the level scheme and the energy-dependent excitation cross section of 76Ge has been investigated. The lack of data inventory for natural germanium has been improved significantly. To enable the investigation of the 76Ge level scheme and the access to a range of other experiments, a powerful, very special requirements corresponding pneumatic tube system was developed and installed in scope of this work at the neutron laboratory of the TU Dresden. Another neutron physics experiment examined the so far unobserved electroncapture of 76As. This shows one way to determine transition matrix elements experimentally, which is often only accessible through theoretical models and prone to large uncertainties. These Matrix elements play a crucial role in the analysis of experiments on double beta decay, in particular the GERDA experiment.