Gamow-Teller strength in theMg26(p,n)26Al reaction at 135 MeV and its fractionation intoT= 0, 1, and 2 isospin channels

The excitation-energy distribution of transition strength to $1^{+}$ states excited via the ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$(p,n${)}^{26}$Al reaction at 134.4 MeV was measured for excitation energies up to 25 MeV. The structures observed in the neutron spectra with ΔL=0 angular distributions were identified as $1^{+}$ states, except for the isobaric analog transition. The total $1^{+}$ strength in this reaction was extracted by normalizing the intensity of the four lowest $1^{+}$ states to the strength measured for the analogous beta decays to these states. A detailed comparison of the experimental results with known analogous transitions and with a large-basis shell-model calculation leads to the conclusion that strengths to states of isospin T=0, 1, and 2 were observed in this reaction. The apportionment of the observed strength among the three isospin values is compared with the shell-model prediction. The total strength observed to all states below an excitation energy of 15 MeV is 57 percent of the total strength predicted by the shell-model calculation with the assumption of the ‘‘free-nucleon’’ normalization of the Gamow-Teller beta decay operator.