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The half-life of \tsups{37}K has been measured to be$1.23651(94)~\mathrm{s}$, a value nearly an order of magnitude more precisethan the best previously reported. The $\beta^+$ decay of \tsups{37}K occursmainly via a superallowed branch to the ground-state of its $T=1/2$ mirror,\tsups{37}Ar. This transition has been used recently, together with similartransitions from four other nuclei, as an alternative test of CVC and methodfor determining $V_{ud}$, but the precision of its $ft$ value was limited bythe relatively large half-life uncertainty. Our result corrects that situation.Another motivation for improving the $ft$ value was to determine thestandard-model prediction for the $\beta$-decay correlation parameters, whichwill be compared to those currently being measured by the \trinat{}collaboration at \triumf. The new $ft$ value, $4605(8)~\mathrm{s}$, is nowlimited in precision by the $97.99(14)\%$ ground-state branching ratio.

Precision half-life measurement of the \boldmath$\beta^+$ decay of \tsups{37}K