Isobaric-Spin Selection Rule in theB10(d,α)Be8Reaction at 7.5 MeV

Angular distributions were measured for the ${\mathrm{B}}^{10}(d,\alpha ){\mathrm{Be}}^8$ reaction leading to the ${\mathrm{Be}}^8$ levels at 16.62, 16.92, 17.64, and 18.15 MeV. The fact that the total cross section to the 16.62-MeV state is about 115% of that to the 16.92-MeV state shows that, as was revealed earlier for lower bombarding energies, there is a large violation of the isobaric-spin selection rule. The total cross section to the 18.15-MeV state is about 85% of that to the 16.92-MeV state, but the total cross section to the 17.64-MeV state is about 7% of it. Isobaric spin thus does not appear to be a good quantum number for the 16.62- and 16.92-MeV levels, but the 17.64-MeV level does seem to be a nearly pure $T=1\mathrm{}$ state.