After qualitative discussion of what can be expected in quasielastic ($\pi , {\pi }^{\prime }$) experiments, a semiclassical model is developed. The mean free path for pion absorption in nuclear matter is a more or less unknown ingredient of the model, but the predictions for the effective nucleon number are insensitive to it. The uncertainties of nuclear corrections can be largely avoided by considering ratios of quasielastic cross sections between different nuclei.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}(\pi , {\pi }^{\prime })$, quasielastic scattering; $T_{\pi }=100-400\mathrm{}$ MeV; calculated $\sigma \left(\theta \right)$, semiclassical model; ratios of $\sigma \left(\theta \right)\text{'}\mathrm{s}$.

• Received 25 November 1974

DOI:https://doi.org/10.1103/PhysRevC.11.1610