Background: The precise determination of $ft$ values for superallowed mixed transitions between mirror nuclide are gaining attention as they could provide an avenue to test the theoretical corrections used to extract the $V_{ud}$ matrix element from superallowed pure Fermi transitions. The ${}^{17}\mathrm{F}$ decay is particularly interesting as it proceeds completely to the ground state of ${}^{17}\mathrm{O}$, removing the need for branching ratio measurements. The dominant uncertainty on the $ft$ value of the ${}^{17}\mathrm{F}$ mirror transition stems from a number of conflicting half-life measurements.

Purpose: A precision half-life measurement of ${}^{17}\mathrm{F}$ was performed and compared to previous results.

Methods: The life-time was determined from the β counting of implanted ${}^{17}\mathrm{F}$ on a Ta foil that was removed from the beam for counting. The ${}^{17}\mathrm{F}$ beam was produced by transfers reaction and separated by the TwinSol facility of the Nuclear Science Laboratory of the University of Notre Dame.

Results: The measured value of $t_{1/2}^{\text{new}}=64.402$(42) s is in agreement with several past measurements and represents one of the most precise measurements to date. In anticipation of future measurements of the correlation parameters for the decay and using the new world average $t_{1/2}^{\text{world}}=64.398$(61) s, we present a new estimate of the mixing ratio $\rho$ for the mixed transition as well as the correlation parameters based on assuming Standard Model validity.

Conclusions: The relative uncertainty on the new world average for the half-life is dominated by the large ${\chi }^2=31$ of the existing measurements. More precision measurements with different systematics are needed to remedy to the situation.

• Received 8 December 2015

DOI:https://doi.org/10.1103/PhysRevC.93.025503