Compound nucleus formation in reactions between massive nuclei. Fusion barrier

The evaporation residue cross sections σER in reactions between massive nuclei have been analyzed within different models of complete fusion. The calculations in the framework of the optical model, the surface friction model and the macroscopic dynamic model can give the results which are by few orders of magnitude different from experimental data. This takes place due to neglect of the competition between complete fusion and quasifission. A possible mechanism of compound nucleus formation in heavy ion-induced reaction has been suggested. A model is proposed for calculation of this competition in a massive symmetric dinuclear system. This model is applied for collision energies above the Coulomb barrier. The σER values calculated in the framework of the approach suggested seem to be close to the experimental data. For illustration the reactions 100Mo + 100Mo, 110Pd + 110Pd and 124Sn + 96Zn have been considered. 35 refs., 6 figs