Precise half-life measurement of the superallowed ${\beta }^{+}$ emitter ${}^{38}\mathrm{K}$${}^m$

The half-life of ${}^{38}\mathrm{K}$${}^m$ has been measured to be 924.46(14) ms, a result that is a factor of two more precise than any of the five previous measurements of this quantity. The previous results are not consistent with one another, but our result agrees well with the two most recent ones. The derived $\mathit{ft}$ value for ${}^{38}\mathrm{K}$${}^m$ is now one of the three most precisely known superallowed $\mathit{ft}$ values.

Figure 1

The ${}^{38}\mathrm{K}$${}^m$ half-life results. The top panel shows a typical dead-time-corrected decay curve from a single run summed over 128 cycles. The bottom panel shows the half-life results (with statistical errors) obtained with MCS1 for all 31 runs.

Figure 2

Half-life measurements of ${}^{38}\mathrm{K}$${}^m$ (with statistical uncertainties) sorted by adjustable electronic and experimental settings. All reduced ${\chi }^2$ values for the independent groups are less than unity.

Figure 3

The data points represent all published measurements of the ${}^{38}\mathrm{K}$${}^m$ half-life with quoted uncertainties that are within a factor of 10 of the present measurement. The results are plotted in chronological order from left to right in the same order as they appear in Table . The weighted average, 924.33 ms, is given by the horizontal line, with its scaled uncertainty, $\pm 0.27$ ms, represented by the gray band. Note that the uncertainty on the average has been increased by a scale factor equal to the square root of the reduced ${\chi }^2$ for all six results, which is 4.83.