High-precision measurement of a low Q value for allowed $\beta^-$-decay of $^{131}$I related to neutrino mass determination
Résumé
The ground-state-to-ground-state -decay 131I (7/2+) → 131Xe (3/2+) Q value was determined with high precision utilizing the double Penning trap mass spectrometer JYFLTRAP at the IGISOL facility. The Q value of this -decay was found to be Q = 972.25(19) keV through a cyclotron frequency ratio measurement with a relative precision of 1.6 × 10−9. This was realized using the phase-imaging ion-cyclotron-resonance technique. The new Q value is more than 3 times more precise and 2.3σ higher (1.45 keV) than the value extracted from the Atomic Mass Evaluation 2020. Our measurement confirms that the -decay to the excited state at 971.22(13) keV in 131Xe is energetically allowed with a Q value of 1.03(23) keV while the decay to the state at 973.11(14) keV was found to be energetically forbidden. Nuclear shell-model calculations with established two-body interactions, alongside an accurate phase-space factor and a statistical analysis of the logft values of known allowed β decays, were used to estimate the partial half-life for the low-Q-value transition to the state. The half-life was found to be () years, which makes this candidate feasible for neutrino mass searches.