Differential cross sections were measured for ${\pi }^{-}$-carbon scattering at 69.5 and 87.5 Mev and ${\pi }^{-}$-oxygen scattering at 87.5 Mev from 20° to 125° extending the technique of Baker, Rainwater, and Williams. The energy resolution was sufficient to measure pure elastic as well as 5- and 10-Mev inelastic cross sections. The modified Kisslinger optical-model equation was used to fit the elastic-cross-section data. A ${\chi }^2$ analysis for the 69.5-Mev carbon data gave a nuclear radius parameter $r_0=1.05\mathrm{}\pm 0.02$ fermis and a fall-off parameter $t=1.16\mathrm{}\pm 0.07$ fermis. These parameters give good fits to the other data as well. An energy dependence in the strength parameters for carbon is observed in qualitative agreement with prediction.

• Received 29 November 1960

DOI:https://doi.org/10.1103/PhysRev.122.252