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Abstract

The observation of neutrinoless double-electron capture would prove the Majorana character of neutrinos. Transitions with an energy degeneracy of the initial and final state show a resonant enhancement of the decay rate and would be important for neutrino physics experiments. In order to identify such transitions, precise Q-value measurements with Penning-trap mass spectrometers play a key role. In this thesis, the resonance condition of neutrinoless double-electron capture in ¹⁰⁶Cd, ¹⁰⁸Cd, and ¹⁸⁴Os was investigated by Q-value measurements with the Penning-trap mass spectrometer TRIGA-TRAP. In addition, the Q value of the double-beta decay in ¹¹⁰Pd was measured. A high-voltage platform and an on-line ion source for the ionization of shortlived neutron-rich fission products for the TRIGA-SPEC experiment located at the research reactor TRIGA Mainz has been commissioned and tested. The aim is to provide a radioactive ion beam for high-precision mass spectrometry and collinear laser spectroscopy. For the extraction from the TRIGA reactor, the fission products are attached to aerosol particles and transported with a gas-jet system to the on-line ion source. This ion source has to cope with a high gas load and has to destroy the bond between fission product and aerosol particle. It was investigated, whether an 2.45 GHz ECR ion source is suited for this task.