Authors
Gamage, N.; Sandler, R.; Buchinger, F.; Clark, J.; Ray, D.; Orford, R.; Porter, W.; Redshaw, M.; Savard, G.; Sharma, K.; Valverde, A.
Abstract
Background: An ultralow Q-value /3 decay can occur from a parent nuclide to an excited nuclear state in the daughter such that QUL <= 1 keV. These decay processes are of interest for nuclear /3-decay theory and as potential candidates in neutrino mass determination experiments. To date, only one ultralow Q-value /3 decay has been observed-that of 115In with Q/3 = 147(10) eV. A number of other potential candidates exist, but improved mass measurements are necessary to determine if these decay channels are energetically allowed and, in fact, ultralow.Purpose: To perform precise /3-decay Q-value measurements of 112,113Ag and 115Cd and to use them in combination with nuclear energy level data for the daughter isotopes 112,113Cd and 115In to determine if the potential ultralow Q-value /3-decay branches of 112,113Ag and 115Cd are energetically allowed and <= 1 keV.Method: The Canadian Penning Trap at Argonne National Laboratory was used to measure the cyclotron frequency ratios of singly charged 112,113Ag and 115Cd ions with respect to their daughters 112,113Cd and 115In. From these measurements, the ground-state to ground-state /3-decay Q values were obtained.Results: The 112Ag -> 112Cd, 113Ag -> 113Cd, and 115Cd -> 115In /3-decay Q values were measured to be Q/3(112Ag) = 3990.16(22) keV, Q/3(113Ag)= 2085.7(4.6) keV, and Q/3(115Cd) = 1451.36(34) keV. These results were compared to energies of excited states in 112Cd at 3997.75(14) keV, 113Cd at 2015.6(2.5) and 2080(10) keV, and 115In at 1448.787(9) keV, resulting in precise QUL values for the potential decay channels of -7.59(26 ) keV, 6(11) keV, and 2.57(34) keV, respectively.Conclusion: The potential ultralow Q-value decays of 112Ag and 115Cd have been ruled out. 113Ag is still a possible candidate until a more precise measurement of the 2080(10) keV, 1/2+ state of 113Cd is available. In the course of this work we have found the ground state mass of 113Ag reported in the 2020 Atomic Mass Evaluation [Wang et al., Chin. Phys. C 45, 030003 (2021 to be lower than our measurement by 69(17) keV (a 4a discrepancy).