Cluster structure of O17

Abstract

The transfer reaction $^{13}\mathrm{C}(^{11}\mathrm{B},^{7}\mathrm{Li})^{17}\mathrm{O}$ leading to the ground and several excited states of $^{17}\mathrm{O}$ was investigated at an incident boron beam energy of 45 MeV. The experimental data were analyzed by means of coupled-channel Born approximation calculations and $^{17}\mathrm{O}=\ensuremath{\alpha}+^{13}\mathrm{C}$ spectroscopic factors were extracted from a comparison of the data and the calculations at forward angles. The largest spectroscopic factor obtained was that for the subthreshold 6.356 MeV $1/{2}^{+}$ state, important for the production of neutrons in the stellar environment, and the squared Coulomb modified asymptotic normalization coefficient, ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{C}}^{2}$, is consistent with previous determinations. A significant rise in the experimental data at backward scattering angles suggested the possibility of $^{17}\mathrm{O}=^{6}\mathrm{Li}+^{11}\mathrm{B}$ clustering in some $^{17}\mathrm{O}$ states, including the ground state. However, explicit inclusion of $^{6}\mathrm{Li}$ transfer in the calculations could not explain the observed effect. Compound nucleus calculations suggested that while the backward angle rise could be explained by such processes for two of the populated $^{17}\mathrm{O}$ states other multistep direct processes must contribute significantly to the other two.