$Q_{\mathrm{EC}}$ Values of the Superallowed $\beta$ Emitters ${}^{50}\mathrm{Mn}$ and ${}^{54}\mathrm{Co}$

Using a new fast cleaning procedure to prepare isomerically pure ion samples, we have measured the beta-decay $Q_{\mathrm{EC}}$ values of the superallowed $\beta$ emitters ${}^{50}\mathrm{Mn}$ and ${}^{54}\mathrm{Co}$ to be 7634.48(7) and 8244.54(10) keV, respectively, results which differ significantly from the previously accepted values. The corrected $\mathcal{F}t$ values derived from our results strongly support new isospin-symmetry-breaking corrections that lead to a higher value of the up-down quark mixing element $V_{ud}$ and improved confirmation of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

Figure 1

Schematic of the full cycle to perform a cyclotron frequency measurement with an isomerically clean sample of ions.

Figure 2

Time-of-flight cyclotron resonances obtained using excitation with time-separated oscillatory fields. An excitation time pattern of 25-150-25 ms (on-off-on) was used. The vertical bars denote the cyclotron resonance frequencies ${\nu }_c$. Gray shading around the data points indicates the number of ions in each time-of-flight bin: the darker the gray, the more ions.

Figure 3

Individual measurements for the ${}^{54}\mathrm{Co}\mathrm{\text{−}}{}^{54}\mathrm{Fe}$ $Q_{\mathrm{EC}}$ value. Sets (a)–(c) were obtained with conventional 200-ms rf excitation but with different cleaning settings for each set. Sets (d) and (e) were both obtained with an excitation time pattern of 25-150-25 ms (on-off-on) but with different magnetron excitation amplitudes. The result labeled (f) is the $Q_{\mathrm{EC}}$-value result from the isomer-daughter and isomer-to-ground-state pairs. The light gray bands denote the average of each set; the dark gray band is the final average including all the data.

Figure 4

Previous measurements of the $Q_{\mathrm{EC}}$ values of ${}^{50}\mathrm{Mn}$ and ${}^{54}\mathrm{Co}$ compared to the present results. The letters on the horizontal scale refer to the sources: (a) Hoath et al. [21]; (b) Hardy et al. [22]; (c) Vonach et al. [7]; and (d) this work. The gray bar is the value adopted in 1, including not only the data shown but also the measurements of $Q_{\mathrm{EC}}$-value differences [23].

Figure 5

$\mathcal{F}t$-value results for the 13 best known superallowed decays, to which the new isospin-symmetry-breaking corrections [3] have been applied. For the ${}^{50}\mathrm{Mn}$ and ${}^{54}\mathrm{Co}$ cases, the points shown in gray are the values that were obtained using the previously accepted $Q_{\mathrm{EC}}$ values; those in black result from the new $Q_{\mathrm{EC}}$ values reported in this work.