Measurements of positive-pion elastic scattering cross sections at 20 MeV have been made in the angular range 30°-150°. Angular distributions were obtained for targets of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. The data were fit with a phenomenological optical model potential calculation to obtain the real and imaginary $s$- and $p$-wave strength parameters. These parameters are compared to those obtained from data at 30, 40, and 50 MeV. Cross sections calculated from an optical model potential based on pionic atom data are in good agreement with our data at 20 MeV.

NUCLEAR REACTIONS Elastic scattering of 20-MeV ${\pi }^{+}$ from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. Angular distributions $30°\le {\theta }_L\le 160°$. Optical model analysis of differential cross sections.

• Received 8 December 1982

DOI:https://doi.org/10.1103/PhysRevC.27.2753