π∓,πNknockout reactions onN14from 50 to 90 MeV

The cross sections for the knockout reactions ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({\pi }^{-},{\pi }^{-}n){}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}({\pi }^{+},{\pi }^{+}n+{\pi }^{0}p){}_{}{}^{13}{}_{}{}^{}\mathrm{N}$ were measured over the energy range of 50 to 90 MeV by an activation method. The ratio of the cross sections $\frac{\sigma \left(\pi {}_{}{}^{14}{}_{}{}^{}\mathrm{N}\right)}{\sigma \left(\pi {}_{}{}^{12}{}_{}{}^{}\mathrm{C}\right)}$ at 70 and 90 MeV for both ${\pi }^{+}$ and ${\pi }^{-}$ is in good agreement with the similar ratio from high energy $p,pn$ reactions on the same targets. This is consistent with a quasifree pion-nucleus knockout picture. However, the ratio $\frac{\sigma \left({\pi }^{-}{}_{}{}^{14}{}_{}{}^{}\mathrm{N}\right)}{\sigma \left({\pi }^{+}{}_{}{}^{14}{}_{}{}^{}\mathrm{N}\right)}$ found to be about a third of the free pion-nucleon ratio, is in disagreement with the simple impulse approximation model.