Gamow-Teller strength in ß-decay of ²⁵Si

The β-rays and β-delayed protons following the decay of ²⁵Si have been studied using a recoil mass separator and highly efficient ß- and proton-detector systems. A new proton transition of 0.403 MeV has been assigned to the decay of ²⁵Al. The proton spectra have given the relative ß-feeds of the proton-unbound levels in ²⁵Al and the ß-ray measurements the summed feed of the proton-bound states. From these results, the ß-decay branching ratios of ²⁵Si to the state of up to 9.42 MeV in ²⁵Al are derived exclusively on the experimental basis. The branching ratios are then converted to the Gamow-Teller (GT) strengths and compared, together with the level structure of ²⁵Al, with the large-scale shell-model calculation. The results have shown an excellent predictability of the shell-model calculation both in level energies and in relative variation of the GT strengths below 6 MeV of excitation in ²⁵Al. For high-lying states, the disagreements between the experimental results and the calculation become large, and consequently the reasonable basis for deriving the quenching factor of the GT strength by using the shell-model calculation seems to be lost.