Superallowed Branching Ratio in the $\beta $ Decay of $^{34}$Ar

Precise \textit{ft}-values for superallowed $0^+\to 0^+ \quad \beta ^{+}$-decays contribute to the most demanding unitarity test of the Cabibbo-Kobayashi-Maskawa matrix. The decays from T$_{z}$=-1 nuclei, like $^{34}$Ar, are particularly valuable because they can constrain the isospin symmetry-breaking corrections that must be applied to the measured \textit{ft}-values. This requires their branching ratios to be determined to $\sim $0.1{\%} or better. We report here on our continuing quest to reach this goal, which most recently has involved better control of our detection geometry (with laser ranging) and continuous monitoring of dead-time. We produced a pure $^{34}$Ar beam at the exit of the MARS recoil separator using a 25A MeV $^{35}$Cl beam from the Texas A{\&}M cyclotron to bombard a hydrogen gas target. The $^{34}$Ar beam was extracted into air, degraded and implanted into the Mylar tape of our fast transport system. In repeated cycles, each $^{34}$Ar sample was collected for 2s and then moved in 175 ms to the center of a well-shielded $\beta -\gamma $ counting station, where $\beta $ singles and $\beta -\gamma $ coincidences were recorded for 2s. The $\beta $'s were detected in a1-mm-thick plastic scintillator, while the $\gamma $'s were detected by our precisely efficiency-calibrated HPGe detector. With the laser sensor we read the tape-to-HPGe distance to a precision better than 0.1mm and recorded it for each cycle. Branching-ratio results will be reported.