EVIDENCE FOR ONE-PION CHARGE-EXCHANGE IN N-13-13 ELASTIC-SCATTERING NEAR THE COULOMB BARRIER(C)

Elastic N-13 + C-13 cross sections are measured at center-of-mass ener gies of 8.15, 10.0, and 14.75 MeV, using a radioactive N-13 beam and p osition-sensitive solid-state detectors. The N-13 + C-13 angular distr ibutions display oscillations beyond 80 degrees and even a significant rise at large angles for the two higher energies. These data are anal yzed in the framework of the optical model including a parity-dependen t term necessary to explain the backward behavior. This parity term is among the strongest encountered in heavy-ion collisions. Its properti es are close to those of the parity term reproducing the N-13 + C-12 e lastic scattering in the same energy range. Its long-range nature indi cates that the parity dependence arises from a single rather than from a double exchange. One-pion charge exchange between the valence nucle ons seems to possess the necessary properties as qualitatively shown b y a simple molecular model.