Direct determination of the atomic mass difference of the pairs and rules out and as possible candidates for electron (anti)neutrino mass measurements
Résumé
The first direct determination of the ground-state–to–ground-state values of the decay and the electron-capture decay was performed utilizing the double Penning trap mass spectrometer JYFLTRAP. By measuring the atomic mass difference of the decay pairs via the phase-imaging ion-cyclotron-resonance technique, the values of and were determined to be 2959.265(74) keV and 814.94(18) keV, respectively. The precision was increased relative to earlier measurements by factors of 12 and 57, respectively. The new values are 1.33 keV and 5 keV lower compared to the values adopted in the most recent Atomic Mass Evaluation 2020. With the newly determined ground-state–to–ground-state values combined with the excitation energy from -ray spectroscopy, the values for ground-state–to–excited-state transitions (ground state) (2968.4(7) keV) and (ground state) (815.731(3) keV) were derived to be keV and keV. Thus we have confirmed that both of the -decay and EC-decay candidate transitions are energetically forbidden at a level of at least , thus definitely excluding these two cases from the list of potential candidates for the search of low--value or EC decays to determine the electron-(anti)neutrino mass.