Precise Mass Measurements of A=133 Isobars with the Canadian Penning Trap: Resolving the Q_β^- anomaly at ^133Te

We report precision mass measurements of ^133Sb, ^133g,mTe, and ^133g,mI, produced at CARIBU at Argonne National Laboratory's ATLAS facility and measured using the Canadian Penning Trap mass spectrometer. These masses clarify an anomaly in the ^133Te β-decay. The masses reported in the 2020 Atomic Mass Evaluation (M. Wang et al., 2021) produce Q_β^-(^133Te)=2920(6) keV; however, the highest-lying ^133I level populated in this decay is observed at E_i=2935.83(15) keV, resulting in an anomalous Q_β^-^i=-16(6) keV. Our new measurements give Q_β^-(^133Te)=2934.8(11) keV, a factor of five more precise, yielding Q_β^i=-1.0(12) keV, a 3σ shift from the previous results. This resolves the anomaly and indicates the possibility of an ultralow Q-value β decay in this system.