The total fusion cross sections for ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$+${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ were measured in the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ bombarding energy range 35-60 MeV in 5 MeV steps by detecting the evaporation residues with a gas ionization $E-\Delta E$ detector. The measured fusion cross sections are significantly smaller than the total reaction cross sections calculated using optical model parameters obtained from fitting the elastic scattering cross sections in the same energy range. Similar results were obtained earlier for the case of ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$+${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ fusion. The fact that ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ is weakly bound and is easily dissociated in the Coulomb and nuclear fields of either the ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ or ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ nucleus is believed to have a strong influence on the observed fusion and elastic scattering cross sections. Sources of possible discrepancy between fusion cross sections measured by determining the yield of heavy evaporation residues and those by summing the cross sections for the emission of light particles such as protons, neutrons, and alpha particles from the compound system are discussed.

NUCLEAR REACTIONS ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$+${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ fusion, $E\left({}_{}{}^9{}_{}{}^{}\mathrm{Be}\right)=35, 40, 45, 50, 55, 60$ MeV, detected evaporation residues, deduced total fusion cross sections, calculated ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$+${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ total reaction cross sections.

• Received 8 November 1982

DOI:https://doi.org/10.1103/PhysRevC.27.1807