The interaction of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ ions with ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ target nuclei was investigated by measuring elastic scattering cross sections and evaporation spectra. The behavior of the elastic scattering cross sections as a function of the classical distance of closest approach indicates a localization of direct reaction processes in the far tail region of the interaction potential, whereas fusion with compound nucleus formation sets in at considerably shorter distances. A statistical model analysis of the evaporation spectra led to a value of ${\sigma }_{\mathrm{fus}}=735\mathrm{}$ mb for the fusion cross section, whereas the total reaction cross section as determined from the elastic scattering data amounts to ${\sigma }_R=1120\mathrm{}$ mb. This difference is a peculiar phenomenon of the very weakly bound ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ system.

NUCLEAR REACTIONS ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ (${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$), (${}_{}{}^9{}_{}{}^{}\mathrm{Be},\alpha$), (${}_{}{}^9{}_{}{}^{}\mathrm{Be},p$), $E_{\mathrm{lab}}=20\mathrm{}$ MeV, measured $\sigma (E,\theta )$, deduced ${\sigma }_{\mathrm{fus}}$, ${\sigma }_R$.

• Received 11 April 1977

DOI:https://doi.org/10.1103/PhysRevC.17.2106