The superallowed β-decay of 18Ne, 22Mg and 26Si

The decays of 18Ne, 22Mg and 26Si have been studied in experiments that employed a gas-transport system to reduce background activities. Through observation of the spectra of β-delayed γ-rays, the half-lives of the three nuclei were measured to be 1687 ± 9, 3857 ± 9 and 2210 ± 21M ms, respectively, and the branching ratios of the respective superallowed transitions were determined to be (7.66 ± 0.21), (54.0 ± 1.1) and (74.9 ± 0.9) %. The resulting ft values give no indication of significant charge-dependent mixing, and comparison with the decay of 26mAl yields a mirror asymmetry for mass 26 of Δ = (−0.8 ± 1.5)%. These results are consistent with expectations. In addition, the ft values for a number of Gamow-Teller transitions have been established.