ENTRANCE CHANNEL EFFECTS IN FUSION-EVAPORATION PROCESSES

The effect of shape equilibration on particle emission in fusion react ions is thoroughly studied. Following a detailed evaluation of the var ious time scales a microscopic dynamical picture of the fusion path is coupled to a statistical decay probability at different time steps. I t is shown that excitation energy and deformation of the compound syst em are influencing the emission pattern of charged particles and Giant Dipole photons. A quantitative analysis is performed for a Yb-164 com pound system formed via O + Sm (mass asymmetric) and Ni + Mo (mass sym metric) channels at various excitation energies. In the mass-symmetric case interesting effects are revealed on spectra and angular distribu tions of emitted particles, particularly for a's, protons and Giant Di pole photons. Experiments are suggested to directly measure these ''pr e-equilibrium'' contributions leading to new information on very exoti c hyperdeformed nuclear systems. (C) 1998 Elsevier Science B.V.