The cross sections for the knockout reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{-},{\pi }^{-}n){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+},{\pi }^{+}n+{\pi }^{0}p){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ were measured over the energy range of 30 to 90 MeV by an activation method. These data together with previous data at higher energies are compared to existing impulse-model calculations. These calculations give general agreement with the shape of the excitation curve for $\sigma \left({\pi }^{-12\mathrm{}}\mathrm{C}\right)$ and poorer agreement for $\sigma \left({\pi }^{+12\mathrm{}}\mathrm{C}\right)$. In the energy range of 30 to 90 MeV, the ratio $\frac{\sigma \left({\pi }^{-12\mathrm{}}\mathrm{C}\right)}{\sigma \left({\pi }^{+12\mathrm{}}\mathrm{C}\right)}$ of the cross sections is 2 to 3 times smaller than the corresponding ratio for pions on nucleons, contrary to the expectations of the simple impulse approximation. This discrepancy has previously been known only near the energy of the (3, 3) resonance.

• Received 17 April 1973

DOI:https://doi.org/10.1103/PhysRevC.8.2039