Two-step contributions and non-orthogonality effects in deuteron and 17O reactions on lead

A numerically stable and accurate method to calculate non-orthogonality terms has been incorporated in a general coupled-channels program that allows finite range transfer couplings between any number of light or heavy ions. The non-orthogonality terms have been calculated for the two-step transfer contributions to deuteron elastic scattering and to 17O inelastic scattering on lead, at energies near the Coulomb barrier. It is found that the sequential amplitudes through the weakly bound states in 209Pb are especially affected, as these amplitudes are over-estimated by between 30 % and 150 % in simple post-prior calculations. These effects are observable because the more direct processes are not too strong, and a good fit is now obtained to the data of Lilley et al. (author)