High-precision half-life measurements of the T=1/2 mirror β decays F17 and Cl33

Background: Measurements of the ft values for T=1/2 mirror β+ decays offer a method to test the conserved vector current hypothesis and to determine Vud, the up-down matrix element of the Cabibbo-Kobayashi-Maskawa matrix. In most mirror decays used for these tests, uncertainties in the ft values are dominated by the uncertainties in the half-lives. Purpose: Two precision half-life measurements were performed for the T=1/2β+ emitters, F17 and Cl33, in order to eliminate the half-life as the leading source of uncertainty in their ft values. Method: Half-lives of F17 and Cl33 were determined using β counting of implanted radioactive ion beam samples on a moving tape transport system at the Système de Production d'Ions Radioactifs Accélérés en Ligne low-energy identification station at the Grand Accélérateur National d'Ions Lourds. Results: The F17 half-life result, 64.347 (35) s, precise to ±0.05%, is a factor of 5 times more precise than the previous world average. The half-life of Cl33 was determined to be 2.5038 (22) s. The current precision of ±0.09% is nearly 2 times more precise compared to the previous world average. Conclusions: The precision achieved during the present measurements implies that the half-life no longer dominates the uncertainty of the ft values for both T=1/2 mirror decays F17 and Cl33.