The sub-barrier fusion cross section for the weakly bound neutron system ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$+${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ is discussed in the framework of the coupled-reaction-channel (CRC) approach for the valence neutron in ${}_{}{}^{11}{}_{}{}^{}\mathrm{Be}$ and in connection with the molecular orbital formation. In the calculation we observe a big enhancement of the fusion process as well as the formation of a covalent molecule (${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}+n+{}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$) due to very strong multistep processes in the inelastic and transfer transitions of the active neutron. As a consequence of the strong CRC effects sharp resonances are observed as fine structure of the fusion cross section, in the case that the absorption effects of the internuclear potential are weak.

• Received 29 March 1995

DOI:https://doi.org/10.1103/PhysRevC.52.3249