New Nuclear Structure and Decay Results in the 76Ge-76As System

The process of neutrinoless double beta decay (0 nu beta beta) plays a key role in modern neutrino physics. Experiments on Ge-76 0 nu beta beta-decay using germanium semiconductors are at the forefront in this field. Due to the extremely low count rates expected for this rare decay, any kind of background event in the detector, especially at energies close to Q(beta beta) = 2039.006 keV must be avoided. Therefore, a careful investigation on the neutron-induced background was carried out. In this scope experiments investigating the inelastic neutron excitation of the lower lying and the 69th excited level of Ge-76 have been performed. The existence of a 2040.7 keV gamma-ray, that occurs by the de-excitation of the 69th excited level, was confirmed. Interfering background from Ge-68 was studied via cross-section measurements of the Ge-nat(n,jn)Ge-68 reaction using quasi-monoenergetic neutrons and accelerator mass specrometry for Ge-68 detection. In order to explore the matrix element for the transition between the Ge-76-As-76 ground states, the electron capture of As-76 has been measured for the first time.