Pion Production Ratios. II

The ratio of positive to negative pion production is considered for protons of {~}0.35-Bev energy incident on nuclei. The model of a single excited nucleon is used. It is argued that (i) at these energies the meson-producing nucleon state is about equally likely to be T=1/2 or T=3/2; (ii) structural effects in the final nucleus inhibit π^- production in light nuclei, where isotopic spin is conserved. Effect (ii) may be partly responsible for the observed difference in shape of π⁺ and π^- production curves as a function of A.