Ultra-High Precision Half-Life Measurement for the Superallowed $\beta^+$ Emitter $^{26}$Al$^m$

The calculated nuclear structure dependent correction for $^{26}$Al$^m$ ($\delta_{C}-\delta_{NS} = 0.305(27)\%$ [1]) is smaller by nearly a factor of two than the other twelve precision superallowed cases, making it an ideal case to pursue a reduction in the experimental errors contributing to the $\mathcal{F}${\em t} value. An ultra-high precision half-life measurement for the superallowed $\beta^+$ emitter $^{26}$Al$^m$ has been made at the Isotope Separator and Accelerator (ISAC) facility at TRIUMF in Vancouver, Canada. A beam of $\sim 10^5$ $^{26}$Al$^m$/s was delivered in October 2007 and its decay was observed using a 4$\pi$ continuous gas flow proportional counter as part of an ongoing experimental program in superallowed Fermi $\beta$ decay studies. With a statistical precision of $\sim0.008\%$, the present work represents the single most precise measurement of any superallowed half-life to date. \\[4pt] [1] I.S.~Towner and J.C.~Hardy, Phys. Rev. C {\bf 79}, 055502 (2009).