High-precision measurement of a low Q value for allowed β--decay of 131I related to neutrino mass determination

The ground-state-to-ground-state beta(-)-decay I-131 (7/2(+)) -> Xe-131 (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 beta(-)-decay was found to be Q = 972.25(19) keV through a cyclotron frequency ratio measurement with a relative precision of 1.6 x 10(-9). This was realized using the phase-imaging ioncyclotron-resonance technique. The new Q value is more than 3 times more precise and 2.3 sigma higher (1.45 keV) than the value extracted from the Atomic Mass Evaluation 2020. Our measurement confirms that the beta(-)-decay to the 9/2(+) excited state at 971.22(13) keV in Xe-131 is energetically allowed with a Q value of 1.03(23) keV while the decay to the 7/2(+) 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 logf t values of known allowed beta decays, were used to estimate the partial half-life for the low-Q-value transition to the 9/2(+) state. The half-life was found to be (1.97(-0.)(89)(+2.24)) x 10(7) years, which makes this candidate feasible for neutrino mass searches. (C) 2022 The Authors. Published by Elsevier B.V.

Automated summary

The Q value of the ground-state-to-ground-state beta(-)-decay from I-131 to Xe-131 was determined with high precision using the JYFLTRAP double Penning trap mass spectrometer at the IGISOL facility. The new Q value is significantly more precise and higher than previous estimations, confirming the energetically allowed beta(-)-decay to a specific excited state in Xe-131.