Neutron radii determinations from the ratio of. pi. /sup -/ elastic scattering from /sup 12,13/C and /sup 16,18/O

Differential elastic cross-section ratios and absolute cross sections have been measured for /sup 12,13/C at 29.2- and 49.5-MeV average ..pi../sup -/ energy and for /sup 16,18/O at 29.2 MeV. Range telescopes detected the scattered pions. The ratio data were compared with different optical-potential calculations to extract neutron radii of 2.35 +- 0.03 fm for /sup 13/C and 2.81 +- 0.03 fm for /sup 18/O, relative to the neutron radii of /sup 12/C (2.31) and /sup 16/O (2.60), respectively. Our studies indicate little sensitivity to the optical model used.