Backward - Angle Elastic Scattering ofO16onCa40andCa48

Angular distributions at 40 MeV and backward-angle excitation functions in the energy range 25-45 MeV have been measured for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ elastic scattering on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$. The ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ excitation function measured in this experiment shows no indication of the marked structure observed in earlier experiments and predicted by angular-momentum-dependent optical-model calculations. The experimental data are discussed by means of both the standard and the $L$-dependent optical models.