Nadeesha D. Gamage

An ultra-low Q value $β$-decay can occur from a parent nuclide to an excited state in the daughter with $Q_{UL}$ <1 keV. These decays are of interest for nuclear $β$-decay theory and as potential candidates in neutrino mass determination experiments. To date, only one ultra-low Q value $β$-decay has been observed -- that of $^{115}$In with $Q_β$ = 147(10) eV. A number of other potential candidates exist, but improved mass measurements are necessary to determine if the decays are energetically allowed and, in fact, ultra-low. We performed precise $β$-decay Q value measurements of $^{112,113}$Ag and $^{115}$Cd and combined them with nuclear energy level data for the daughter isotopes to determine if the potential UL Q value $β$-decay branches of $^{112,113}$Ag and $^{115}$Cd are energetically allowed and <1 keV. The Canadian Penning Trap at ANL was used to measure the cyclotron frequency ratios of singly-charged $^{112,113}$Ag and $^{115}$Cd ions with respect to their daughters. From these measurements, the ground-state $β$-decay Q values were obtained. The $^{112}$Ag, $^{113}$Ag, and $^{115}$Cd $β$-decay Q values were measured to be 3990.16(22) keV, 2085.7(4.6) keV, and 1451.36(34) keV, respectively. These results were compared to energies of excited states in $^{112}$Cd at 3997.75(14) keV, $^{113}$Cd at 2015.6(2.5) and 2080(10) keV, and $^{115}$In at 1448.787(9) keV, resulting in $Q_{\textrm{UL}}$ values of --7.59(26) keV, 6(11) keV, and 2.57(34) keV, respectively. The potential UL Q value decays of $^{112}$Ag and $^{115}$Cd have been ruled out. $^{113}$Ag is still a possible candidate until a more precise measurement of the 2080(10) keV, 1/2$^{+}$ state of $^{113}$Cd is available. In the course of this work we have found the ground state mass of $^{113}$Ag reported in the 2020AME to be lower than our measurement by 69(17) keV (a 4$σ$ discrepancy).

At Central Michigan University we are developing a high-precision Penning trap mass spectrometer (CHIP-TRAP)that will focus on measurements with long-lived radioactive isotopes. CHIP-TRAP will consist of a pair of hyperbolic precision-measurement Penning traps, and a cylindrical capture/filter trap in a 12 T magnetic field. Ions will be produced by external ion sources, including a laser ablation source, and transported to the capture trap at low energies enabling ions of a given m=q ratio to be selected via their time-of-flight. In the capture trap, contaminant ions will be removed with a mass-selective rf dipole excitation and the ion of interest will be transported to the measurement traps. A phase-sensitive image charge detection technique will be used for simultaneous cyclotron frequency measurements on single ions in the two precision traps, resulting in a reduction in statistical uncertainty due to magnetic field fluctuations.