Isobaric Spin Doublets inBe8Excited with theB10(d,α)Be8Reaction

The $2^{+}$ levels in ${\mathrm{Be}}^8$ at 16.6 and 16.9 MeV were investigated using the ${\mathrm{B}}^{10}(d,\alpha ){\mathrm{Be}}^8$ reaction at several angles and bombarding energies from 4.0 to 12.0 MeV. A pattern of interference between these two levels was observed at all angles and energies except at a deuteron energy of 4.0 MeV. Fits were made to the $\alpha$-particle spectra using two different formulas for the differential cross section. The results are interpreted in terms of the isobaric spin purity of the levels and isobaric spin mixing in the reaction. The latter is found to vary from 4 to 99%. The effects of other $2^{+}$ levels on the 16.6- and 16.9-MeV levels are also discussed. Differential-cross-section ratios of the $1^{+}$ doublet at 17.6 and 18.1 MeV were simultaneously measured. This ratio depends upon deuteron bombarding energy in a way consistent with the change in isobaric spin mixing in the reaction. The $3^{+}$ doublet at 19.05 and 19.22 MeV was investigated. Only one particle group is observed. Various explanations in terms of interference in this region are discussed. The excitation energy and width of the higher $1^{+}$ level were found to be 18.146 ± 0.005 MeV and 138 ± 6 keV, respectively, based on an adopted value of 17.638 MeV for the excitation energy of the lower $1^{+}$ level.