A high-precision half-life measurement for the superallowed ${\beta }^{+}$ emitter ${}^{26}\mathrm{Al}^m$ was performed at the TRIUMF-ISAC radioactive ion beam facility yielding $T_{1/2}=6346.54\pm {0.46}_{\mathrm{stat}}\pm {0.60}_{\mathrm{syst}}\mathrm{ms}$, consistent with, but 2.5 times more precise than, the previous world average. The ${}^{26}\mathrm{Al}^m$ half-life and $ft$ value, 3037.53(61) s, are now the most precisely determined for any superallowed $\beta$ decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected $\mathcal{F}t$ value for ${}^{26}\mathrm{Al}^m$, 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi $\beta$-decay studies used to test the conserved vector current hypothesis and determine the $V_{ud}$ element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.

• Received 20 August 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.032501