Upper limits on the ratio of neutron to proton knockout to the ($2^{+},T=1\mathrm{}$) analog levels in ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ by ${\pi }^{-}$ at 200 MeV are consistent with the nucleon charge exchange model, as modified by nuclear structure considerations. In contrast, the impulse approximation and a semiclassical nucleon charge exchange model give ratios which are larger than the upper bounds. In comparing cross sections involving different final residual nuclei, it is important to consider the relative fragility of the daughter nuclei.

NUCLEAR REACTIONS Ratios (${\pi }^{-},{\pi }^{-}n$) to (${\pi }^{-},{\pi }^{-}p+{\pi }^{0}n$) for ($2^{+},T=1\mathrm{}$) levels, ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, $T_{\pi }=200\mathrm{}$ MeV, detect deexcitation $\gamma \text{'}\mathrm{s}$. Importance of nucleon charge exchange to IAS'S. Relative fragility of daughters.

• Received 23 March 1977

DOI:https://doi.org/10.1103/PhysRevC.16.2059