GIANT-DIPOLE EMISSION AS A PROBE OF THE ENTRANCE CHANNEL DYNAMICS

In this article we focus on specific features associated with the gian t dipole gamma-ray emission from deformed long-living nuclear systems. Solving numerically the Vlasov equation, we follow the fusion path fo r entrance channels with different mass asymmetry in low-energy heavy- ion collisions, just above the fusion threshold, We observe the format ion of long-living deformed compound nuclei in the more symmetric case s. We show that very important features, such as the energy and the an gular correlation of the emitted gamma's, are characteristic effects o f the emission from such deformed systems, For charge-asymmetric chann els we reveal the presence of a new ''direct'' dipole mode, related to the charge equilibration dynamics. From the interplay between charge and the shape equilibration time scales we can suggest new experiments to study the dipole propagation in excited nuclei.