Evidence for one-pion charge exchange in 13N + 13C elastic scattering near the Coulomb barrier.

Abstract

Elastic N-13 + C-13 cross sections are measured at center-of-mass energies of 8.15, 10.0, and 14.75 MeV, using a radioactive N-13 beam and position-sensitive solid-state detectors. The N-13 + C-13 angular distributions display oscillations beyond 80 degrees and even a significant rise at large angles for the two higher energies. These data are analyzed in the framework of the optical model including a parity-dependent term necessary to explain the backward behavior. This parity term is among the strongest encountered in heavy-ion collisions. Its properties are close to those of the parity term reproducing the N-13 + C-12 elastic scattering in the same energy range. Its long-range nature indicates that the parity dependence arises from a single rather than from a double exchange. One-pion charge exchange between the valence nucleons seems to possess the necessary properties as qualitatively shown by a simple molecular model.