High-precision half-life measurement of the β+ decay of Na21

Abstract

The ${\ensuremath{\beta}}^{+}$ decay of $^{21}\mathrm{Na}$ to $^{21}\mathrm{Ne}$ is one of the four cases currently being used to determine the value of ${V}_{\mathrm{ud}}$ from nuclear mirror ($T=1/2$) transitions. To date, published values for the half-life of $^{21}\mathrm{Na}$ have not been consistent with one another. We report here a new measurement of the half-life: $22.4615\ifmmode\pm\else\textpm\fi{}{0.0039}_{(\mathrm{stat})}\ifmmode\pm\else\textpm\fi{}{{}_{0.0015}^{0.0001}}_{(\mathrm{syst})}s$. This result increases the world average of the $^{21}\mathrm{Na}$ half-life by 0.0048 s and reduces the uncertainty by a factor of 1.5.