The dynamical dipole mode in dissipative heavy-ion collisions

We study the effect of a direct giant dipole resonance (GDR) excitation in intermediate dinuclear systems with exotic shape and charge distributions formed in charge asymmetric fusion entrance channels. A related enhancement of the GDR gamma yield in the evaporation cascade of the fused nucleus is expected. The dynamical origin of such GDR extra strength will show up in a characteristic anisotropy of the dipole gamma-emission. A fully microscopic analysis of the fusion dynamics is performed with quantitative predictions of the GDR photon yield based on a dynamics-statistics coupling model. In particular we focus our attention on the energy and mass dependence of the effect, We suggest a series of new experiments, in particular some optimal entrance channel conditions. We stress the importance of using the new available radioactive beams, (C) 2001 Elsevier Science B.V. All rights reserved.