Fusion Cross Sections forα+Ca40,44and the Problem of Anomalous Large-Angle Scattering

Fusion cross sections for the reactions $\alpha$+${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and $\alpha$+${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ have been measured between 10 and 27 MeV (lab) via the detection of the $\gamma$ radiation of the evaporation residues. At maximum the cross sections are about 1170 mb for $\alpha$+${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ and about 970 mb for $\alpha$+${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. This difference supports recent optical-model and semiclassical interpretations that the well-known anomalous large-angle scattering results from different absorption strengths for these two systems.