Interactions of Negative Pions in Carbon and Lead

A cloud chamber investigation of the nuclear interactions of 125-Mev negative pi mesons has been carried out. Carbon and lead were employed as the scattering material. The experimental arrangement was designed to observe the charge-exchange process: ${\pi }^{-}+\mathrm{C}\to {\mathrm{B}}^{\left(\mathrm{exc}\right)}+[{\pi }^0\to 2\gamma ].\mathrm{}$ High-energy photons, probably attributable to charge exchange, are found to arise from nuclear interaction, with a small but finite cross section. Total and differential cross section for elastic and inelastic scattering, as well as total nuclear reaction cross sections, are presented. A square well (optical model) analysis fits the data with a potential whose real part is attractive and 30 Mev deep, and whose imaginary part corresponds to a mean free path in nuclear matter of 3×${10}^{-13\mathrm{}}$ cm. The optical model parameters are found to be energy dependent, the well depth increasing and the mean free path decreasing as the energy is raised.