EFFECTIVE POLARIZATION POTENTIALS AS A TOOL FOR PROBING NEAR-BARRIER REACTION-MECHANISMS

An extensive set of coupled-reaction-channels (CRC) calculations has b een performed for the O-16+Ni-58 and O-16+Ni-62 systems, Derived, effe ctive local polarization potentials for the elastic channels of the tw o systems show energy-dependent behaviour near threshold similar to th at of empirical optical-model potentials. In particular, a peak in the empirical imaginary term in the surface, which was found at approxima tely 10 MeV above the Coulomb barrier, also appears in the calculated potential close to the same energy, The existence of this peak is show n to be due largely to coupling to the first 3(-) state of O-16. Calcu lations generally underpredict the magnitudes of the empirical potenti als, However, agreement is greatly improved if a real polarization pot ential is included in the non-elastic channels in the coupling scheme, This suggests that multi-step processes are important and must be tak en into account even at energies very close to threshold.