Penning trap mass spectrometry Q value determinations for investigating ultra-low Q value β-decays

Ultra-low Q value (ULQ) β-decays, in which the parent decays to an excited state of the daughter with a Q<∼1 keV, are of interest because they can provide a testing ground for atomic interference effects in nuclear β-decay, and because of their potential as candidates for direct neutrino mass determination experiments. The lowest known Q value β-decay is that of ¹¹⁵In to the 3/2⁺ state in ¹¹⁵Sn with Q_β = 155(24) eV. Additional candidates, such as ¹¹⁵Cd and ¹³⁵Cs have been identified by evaluating atomic mass and nuclear energy level data. We have also identified ^112,113Ag, ⁸⁹Sr and ¹³⁹Ba as potential candidates. Current atomic mass data for the parent and/or daughter isotopes in these cases are not precise enough to determine whether the ULQ decay branches are energetically allowed. Here we present preliminary Q value measurement results for ^112,113Ag, ¹¹⁵Cd, ⁸⁹Sr and ¹³⁹Ba using Penning trap mass spectrometry with the CPT mass spectrometer at Argonne National Lab and LEBIT at the National Superconducting Cyclotron Lab.