Study of rare neutron induced processes and coincidence analyses to identify and reduce background contributions in the COBRA experiment

The aim of the COBRA experiment is the observation of neutrinoless double-beta decay, primarily of the isotope ¹¹⁶Cd. The applied semiconductor detectors of cadmium zinc telluride that are 90% to be enriched enable both the detection and the source of this decay. The half-lives of decays of this kind are expected in the range of more than 10²⁶ years. Therefore, the reduction of contributions to the background is of decisive importance. The main subjects of this work are, on the one hand, the time synchronization of the data, which provides the basis for coincidence analysis. This analysis method has access not only to identification of contributions to the background, but also to observe decays involving positron annihilation and decays into excited states. In this study, the intrinsic detector contamination of some decay products of ²³⁸U and ²³²Th was measured and sensitivities to the half-lives of the decays like ¹²⁰Te and ¹²⁸Te in each case to the first excited state of daughter products are given. On the other hand, qualitative studies on the importance of neutrons in the COBRA experiment were conducted. These have shown that fast neutrons, thus with energies greater than 10 keV, only result in an insignificant contribution to the background for the detection of neutrinoless double-beta decay of the ¹¹⁶Cd. Previous studies have also shown that the thermal neutron flux can be in situ determined by coincidence analysis.