Large Angle Scattering of Negative Pions in Aluminum, Copper, and Lead

The total cross sections for backscattering of 32±10 Mev negative pions in Al, Cu, and Pb have been measured. A stripped emulsion was embedded in a semi-infinite absorber, and exposed to an incident beam of ${\pi }^{-}$ mesons. The positions and direction of mesons stopping in the emulsion were recorded. The cross sections are proportional to the ratio of the backward flux to incident flux, both of which are observed on the same strip of emulsion. The conclusions of this investigation are: (a) the scattering is consistent with energy independence in the region of 32±10 Mev; (b) the angular distribution has a maximum at 180°; (c) the cross section for backscattering is proportional to the mass number $A$. The total nuclear backscattering cross sections (elastic and inelastic) for negative pions in Al, Cu, and Pb are 59.6±11 mb, 192±27 mb, and 577±80 mb, respectively.