@phdthesis{Droese2015,
  author    = {Christian Droese},
  title     = {The masses of nobelium and lawrencium isotopes, the mass difference between 180W and 180Hf, and a characterization of the future cryogenic stopping cell of the online mass spectrometer SHIPTRAP},
  journal    = {Die Massen von Lawrencium und Nobelium Isotopen, die Massendifferenz zwischen 180W und 180Hf, und eine Charakterisierung der zuk{\"u}nftigen kryogenen Gasstoppzelle des online Massenspektrometers SHIPTRAP},
  url       = {https://nbn-resolving.org/urn:nbn:de:gbv:9-002149-3},
  year      = {2015},
  abstract  = {This work describes the recent scientific and technical achievements obtained at the high-precision Penning trap mass spectrometer SHIPTRAP. The scientific focus of the SHIPTRAP experiment are mass measurements of short-lived nuclides with proton number larger than 100. The masses of these isotopes are usually determined via extrapolations, systematic trends, predictions based on theoretical models or alpha-decay spectroscopy. In several experiments the masses of the isotopes 252-255No and 255,256Lr have been measured directly. With the obtained results the region of enhanced nuclear stability at the deformed shell closure at the neutron number 152 was investigated. Furthermore, the masses have been used to benchmark theoretical mass models. The measured masses were compared selected mass models which revealed differences between few keV/c² up to several MeV/c² depending on the investigated nuclide and model. In order to perform mass measurements on superheavy nuclei with lower production rates, the efficiency of the SHIPTRAP setup needs to be increased. Currently, the efficiency is 2\% and mainly limited by the stopping- and extraction efficiency of the buffer gas cell. The stopping and extraction efficiency of the current buffer gas cell is 12\%. To this end, a modified version of the buffer gas cell was developed and characterized with 223Ra ion source. Besides a larger stopping volume and a coaxial injection the new buffer gas cell is operated at a temperature of 40K. The operation at cryogenic temperatures increases the cleanliness of the buffer gas. From extraction measurements and simulations an overall efficiency of 62(3)\% was determined which results in an increase by a factor of 5 in comparison to the current buffer gas cell. Aside from high-precision mass measurements of heavy radionuclides the mass differences of metastable isobars was measured to identify candidates for the neutrinoless double-electron capture. Neutrinoless double-electron capture can only occur if the neutrino is its own antiparticle and a physics beyond the standard model exists since the neutrinoless double-electron capture violates the conservation of the lepton number. Due to its expected long half-life this decay has not yet been observed. However, the decay rate is resonantly enhanced if mother and daughter nuclide are degenerate in energy. Suitable candidates for the search of the neutrinoless double-electron capture have been identified with mass difference measurements uncertainties of about 100eV/c². In this work the results of the mass difference measurements of 12 possible candidates are presented.},
  language  = {en}
}