Measurement of Nuclear Energy Levels for Evaluation of Ultra-Low Q Value β-Decays

Ultra-low Q value (ULQ) β-decays are a class of decays where the Q value of the excited daughter isotope Q_es < 1 keV. More specifically, ULQ β-decays occur from the ground state of the parent nucleus to an excited state in the daughter with energy, E*, similar the ground-state Q value, Q_gs, such that Q* = Q_gs – E* < 1 keV. ULQ value β-decays could be used for neutrino mass determination experiments and provide a better understanding of the role of atomic interference effects in β-decay at low energies. We recently surveyed atomic mass and nuclear energy level data to evaluate all potential ULQ decay candidates. However, more precise mass and energy level data is needed. We have added to this study by evaluating potential ULQ decays from long-lived isomers. We will present the study of long-lived isomer ULQ decay candidates and discuss a planned experiment to measure the energy level in ⁷⁵As to help evaluate the potential ULQ electron capture decay of ⁷⁵Se.