RESIDUE EXCITATION-FUNCTIONS FROM COMPLETE FUSION OF O-16 WITH AU-197 AND PB-208

Evaporation residue excitation functions and alpha-multiplicities from complete fusion of O-16 with Au-197 and Pb-208 have been measured from the fusion threshold up to 140 MeV incident energy. The data allow the conclusion that strongly overdamped motion cannot be dominant at energies in the vicinity of the fusion barrier below E* almost-equal-to 50 MeV. At excitation energies above 50 MeV the residue cross section for O-16 + Pb-208 is much greater than predicted from the statistical model with conventional parametrizations. The enhancement is not explained by incorporating dynamical effects into the analysis. An alternative suggestion based on deexcitation-chain dependent fission barriers is discussed.