Positive pion-nucleus elastic scattering at 40 MeV

Differential cross sections for elastic scattering of 40 MeV positive pions from /sup 12/C, /sup 16/O, /sup 40/Ca, /sup 90/Zr, and /sup 208/Pb were measured at 18 angles in the angular range 25/sup 0/--160/sup 0/. Relative uncertainties of 2.5% to 7% and overall normalization uncertainties of 4% to 7% were obtained. An optical potential fit of the data indicates that while the magnitudes of the strength parameters, except for Re b/sub 1/, are different from values obtained from free ..pi..N scattering amplitudes, the variation of these magnitudes with target mass is roughly as predicted by the impulse approximation. Coulomb effects, especially in the cases of /sup 90/Zr and /sup 208/Pb, are extremely important, but impossible to unambiguously separate from the strong interaction in the optical model.