π− elastic scattering on 12,13C and 16,18O at low energies

π− elastic scattering experiments on 12,13C at 29. and 49.5 MeV and on 16,18O at 29. MeV are presented. The ratio of as well as the ratio of 18O differential cross section to 16O differential cross section have been measured. Two optical potentials have been used to examine the sensitivity of the ratios to neutron‐proton radius differences, model dependence and energy dependence.