In pion-nucleus scattering near 50 MeV, the Coulomb and nuclear amplitudes are comparable for a fairly wide range of angles. The interference of these amplitudes makes small nuclear structure effects observable in elastic scattering. As a result, energy dependent optical model analyses of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ do not reproduce the observed 50 MeV cross sections. Including the ground and first excited state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ in a coupled-channel calculation provides a consistent interpretation of both the elastic and inelastic data between 20 and 100 MeV.

• Received 10 October 1985

DOI:https://doi.org/10.1103/PhysRevC.33.1443