Ratios of pion-induced nucleon knockout cross sections are discussed utilizing a modified nucleon charge exchange model which takes into account nuclear structure effects on the effective number of nucleons and on the various probabilities for charge exchange. The availability of particle-stable analog states in the charge exchange transitions can give factor of 2 differences in the neutron knockout ratio between isotopes for a given $Z$. On the other hand, proton knockout ratios are largely independent of nuclear structure. Predictions of the model are in reasonable semiquantitative agreement with all experimental data.

NUCLEAR REACTIONS Ratios of $\sigma (\pi , \pi N)$, $T_{\pi }\approx 190$ MeV, when residual nucleus observed: ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$; ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$; ${}_{}{}^{58,60,62,64}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{64,66,68,70}{}_{}{}^{}\mathrm{Zn}$; ${}_{}{}^{16,17,18}{}_{}{}^{}\mathrm{O}$. Dependence on availability of particle-stable IAS's.

• Received 13 January 1976

DOI:https://doi.org/10.1103/PhysRevC.15.371