Nuclear Interactions of 210-Mevπ−Mesons in Emulsions

A study has been made of the interactions of 210±20-Mev ${\pi }^{-}$ mesons with the nuclei of photographic emulsions which were exposed to the University of Chicago synchrocyclotron. Detailed classification of the events into elastic and inelastic scatterings, stops and stars, permitted some discussion of the mechanisms involved. The mean free path for a nuclear interaction was found to be 25.7 cm, as determined from an examination of 2823 cm of track. The increase in this mean free path over that observed at lower energies at Columbia appears to be primarily due to a decrease in the probability for ${\pi }^{-}$ meson absorption in a nuclear collision.