Effective Polarization Potentials As A Tool for Probing Near-Barrier Reaction Mechanisms

An extensive set of coupled-reaction-channels (CRC) calculations has been performed for the 16O+58Ni and 16O+62Ni systems. Derived, effective local polarization potentials for the elastic channels of the two systems show energy-dependent behaviour near threshold similar to that of empirical optical-model potentials. In particular, a peak in the empirical imaginary term in the surface, which was found at approximately 10 MeV above the Coulomb barrier, also appears in the calculated potential close to the same energy. The existence of this peak is shown to be due largely to coupling to the first 3− state of 16O. Calculations generally underpredict the magnitudes of the empirical potentials. However, agreement is greatly improved if a real polarization potential is included in the non-elastic channels in the coupling scheme. This suggests that multi-step processes are important and must be taken into account even at energies very close to threshold.