Precise Q -value measurements of Ag 112,113 and Cd 115 with the Canadian Penning trap for evaluation of potential ultralow Q -value β decays

N. D. Gamage, R. Sandler, F. Buchinger, J. A. Clark, D. Ray, R. Orford, W. S. Porter, M. Redshaw, G. Savard, K. S. Sharma, A. A. Valverde

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Abstract

Background: An ultralow Q-value β 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 β-decay theory and as potential candidates in neutrino mass determination experiments. To date, only one ultralow Q-value β decay has been observed - that of In115 with Qβ=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 β-decay Q-value measurements of Ag112,113 and Cd115 and to use them in combination with nuclear energy level data for the daughter isotopes Cd112,113 and In115 to determine if the potential ultralow Q-value β-decay branches of Ag112,113 and Cd115 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 Ag112,113 and Cd115 ions with respect to their daughters Cd112,113 and In115. From these measurements, the ground-state to ground-state β-decay Q values were obtained. Results: The Ag112→Cd112, Ag113→Cd113, and Cd115→In115β-decay Q values were measured to be Qβ(Ag112)=3990.16(22) keV, Qβ(Ag113)=2085.7(4.6) keV, and Qβ(Cd115)=1451.36(34) keV. These results were compared to energies of excited states in Cd112 at 3997.75(14) keV, Cd113 at 2015.6(2.5) and 2080(10) keV, and In115 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 Ag112 and Cd115 have been ruled out. Ag113 is still a possible candidate until a more precise measurement of the 2080(10) keV, 1/2+ state of Cd113 is available. In the course of this work we have found the ground state mass of Ag113 reported in the 2020 Atomic Mass Evaluation [Wang, Chin. Phys. C 45, 030003 (2021)1674-113710.1088/1674-1137/abddaf] to be lower than our measurement by 69(17) keV (a 4σ discrepancy).

Original languageEnglish
Article number045503
JournalPhysical Review C
Volume106
Issue number4
DOIs
StatePublished - Oct 2022

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