Excitation Functions for the (${\pi }^{-}, {\pi }^{-}n$) Reaction on ${\mathrm{C}}^{12}$ and ${\mathrm{F}}^{19}$

Cross sections for the reactions ${\mathrm{C}}^{12}({\pi }^{-}, {\pi }^{-}n){\mathrm{C}}^{11}$ and ${\mathrm{F}}^{19}({\pi }^{-}, {\pi }^{-}n){\mathrm{F}}^{18}$ were measured with incident pions of kinetic energy between 0.70 and 1.80 GeV. The results, together with earlier measurements of the former reaction, are compared with a simple model of ($X, \mathrm{XN}$) reactions, assuming a clean knockout of a nucleon $N$ by an incident particle $X$. It is shown that the model does not correctly predict the magnitude of the (${\pi }^{-}, {\pi }^{-}n$) cross sections, although it is successful in predicting the general trend of cross section with energy.