Double-$\beta$ transformations in isobaric triplets with mass numbers $\mathbf{A}=\mathbf{124}$, 130, and 136

The Q values of double-electron capture in ${}^{124}$Xe, ${}^{130}$Ba, and ${}^{136}$Ce and double-beta decay of ${}^{124}$Sn and ${}^{130}$Te have been determined with the Penning-trap mass spectrometer SHIPTRAP with a few hundred eV uncertainty. These nuclides are members of three isobaric triplets with common daughter nuclides. The main goal of this work was to investigate the existence of the resonant enhancement of the neutrinoless double-electron-capture rates in ${}^{124}$Xe and ${}^{130}$Ba in order to assess their suitability for the search for neutrinoless double-electron capture. Based on our results, in neither of these cases is the resonance condition fulfilled.

Figure 1

Schematic experimental setup used for the measurements of the $Q$ values at SHIPTRAP.

Figure 2

Typical time-of-flight ion cyclotron resonances of ${}^{124}$Xe${}^{+}$ (a) and ${}^{130}$Te${}^{+}$ (b) with 25-950-25 ms and 60-2280-60 ms Ramsey excitation patterns, respectively. The solid line is a fit of the theoretical curve to the data points [24].

Figure 3

Cyclotron-frequency ratios of ${}^{130}$Xe${}^{+}$ to ${}^{130}$Ba${}^{+}$ (a) and of ${}^{130}$Xe${}^{+}$ to ${}^{130}$Te${}^{+}$ (b) measured in this work. The grey shaded band represents the total uncertainty of the weighted mean frequency ratio $r_{av}$. Frequency ratios 1 to 15 (a) and 1 to 55 (b) have been measured with a Ramsey pattern of 60-2280-60 ms, whereas a Ramsey pattern of 25-950-25 ms has been employed to measure frequency ratios 16–36 (a) and 56–153 (b). For $r_{av}$ see Tables and .

Figure 4

Cyclotron-frequency ratios of ${}^{124}$Te${}^{+}$ to ${}^{124}$Xe${}^{+}$ (a) and of ${}^{124}$Te${}^{+}$ to ${}^{124}$Sn${}^{+}$ (b) measured in this work. The grey shaded band represents the total uncertainty of the weighted mean frequency ratio $r_{av}$. Frequency ratios 1 to 39 (a) have been measured with a Ramsey pattern of 60-2280-60 ms, whereas a Ramsey pattern of 25-950-25 ms has been employed to measure frequency ratios 40–171 (a) and 1–36 (b). For $r_{av}$ see Tables and .

Figure 5

Cyclotron-frequency ratios of ${}^{136}$Ba${}^{+}$ to ${}^{136}$Ce${}^{+}$ measured in this work. The grey shaded band represents the total uncertainty of the weighted mean frequency ratio $r_{av}$ as cited in Table .

Figure 6

Decay scheme of double-beta decay of ${}^{124}$Sn and double-electron capture in ${}^{124}$Xe, which both end in a common daughter nuclide ${}^{124}$Te. The nuclear excitation energies [31] and $Q$ values measured in this work are given in keV.

Figure 7

Decay scheme of double-beta decay of ${}^{130}$Te and double-electron capture in ${}^{130}$Ba, which proceed to a common daughter nuclide ${}^{130}$Xe. The nuclear excitation energies [44] and $Q$ values measured in this work are given in keV. The assignment of the spin value to the nuclear excited state with energy 2533.4(3) keV was made in this work (see text for details).

Figure 8

Comparison of the $Q$ values of double-beta decay of ${}^{130}$Te obtained by JYFLTRAP [19], the Canadian Penning Trap [20], and the FSU-trap [21] with the $Q$ value of this transition determined in this work, represented by the black line and grey shaded band for the weighted mean and its uncertainty, respectively.

Figure 9

Decay scheme of double-beta decay of ${}^{136}$Xe and double-electron capture in ${}^{136}$Ce. The nuclear excitation energies [46] and $Q$ values are given in keV. The given $Q$ value of double-electron capture in ${}^{136}$Ce is taken from this work whereas the $Q$ value of double-beta decay of ${}^{136}$Xe is taken as the weighted mean of the $Q$ values from Refs. [16, 40].