The observed differential cross section for the process ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}({\pi }^{+}, {\pi }^{-}){}_{}{}^{14}{}_{}{}^{}\mathrm{O}$ at 50 MeV is successfully reproduced in the framework of multiple-scattering theory, with medium effects on $\pi$ and $\Delta$ propagation fitted to elastic $\pi$-${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ scattering.

• Received 26 October 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.1230