$Q_{\mathrm{EC}}$ Values of the Superallowed $\beta$ Emitters ${}^{34}\mathrm{Cl}$ and ${}^{38}\mathbf{K}^m$

The superallowed $\beta$-decay $Q_{\mathrm{EC}}$ values of ${}^{34}\mathrm{Cl}$ and ${}^{38}\mathrm{K}^m$ have been measured with an online Penning trap to be 5491.662(47) keV and 6044.223(41) keV, respectively. The new values are more precise than the previous high-precision reaction-based values but are consistent with them and establish that there are no significant systematic differences between the two types of measurements.

Figure 1

Time-of-flight ion-cyclotron resonance of ${}^{38}\mathrm{K}^m$ obtained with singly charged and isomerically cleaned ions. The resonance was obtained with a (25-350-25) ms (on-off-on) Ramsey excitation-time pattern. The pixels represent detected ions: the darker the pixel, the more ions it represents. The solid (red) line is a fit to the experimental data.

Figure 2

Series of fitted cyclotron frequencies for ${}^{38}\mathrm{K}^m$ and ${}^{38}\mathrm{Ar}$ (lower panel). Each frequency point includes the results of 40 interleaved scans. The top panel shows the deviation of the individual frequency ratios, ${\nu }_d/{\nu }_m$, from the average frequency ratio.

Figure 3

Differences between precise reaction-based and Penning-trap $Q_{\mathrm{EC}}$ value measurements for ${}^{26}\mathrm{Al}^m$, ${}^{34}\mathrm{Cl}$, ${}^{38}\mathrm{K}^m$, and ${}^{42}\mathrm{Sc}$. Only measurements with uncertainties $\le 540\mathrm{eV}$ are included. The ($p$, $n$)-threshold measurements are shown as triangles and are from Refs. 8, 9, 31 (in order from $A=26$ to $A=38$). The $(p,\gamma )+(n,\gamma )$ measurements appear as squares and are from groups of references, which are given in Ref. 1. The gray bands about the zero line represent the uncertainty of the Penning-trap measurements, which are taken from an average of Refs. 3, 32 for ${}^{26}\mathrm{Al}^m$, from this work for ${}^{34}\mathrm{Cl}$ and ${}^{38}\mathrm{K}^m$, and from 3 for ${}^{42}\mathrm{Sc}$.