Entrance channel effects in fusion-evaporation processes

The effect of shape equilibration on particle emission in fusion reactions is thoroughly studied. Following a detailed evaluation of the various time scales a microscopic dynamical picture of the fusion path is coupled to a statistical decay probability at different time steps. It is shown that excitation energy and deformation of the compound system are influencing the emission pattern of charged particles and Giant Dipole photons. A quantitative analysis is performed for a Yb-164 compound system formed via O + Sm (mass asymmetric) and Ni + Mo (mass symmetric) channels at various excitation energies. In the mass-symmetric case interesting effects are revealed on spectra and angular distributions of emitted particles, particularly for a's, protons and Giant Dipole photons. Experiments are suggested to directly measure these "pre-equilibrium" contributions leading to new information on very exotic hyperdeformed nuclear systems. (C) 1998 Elsevier Science B.V.