Giant dipole emission as a probe of the entrance channel dynamics

In this article we focus on specific features associated with the giant dipole γ-ray emission from deformed long-living nuclear systems. Solving numerically the Vlasov equation, we follow the fusion path for entrance channels with different mass asymmetry in low-energy heavy-ion collisions, just above the fusion threshold. We observe the formation of long-living deformed compound nuclei in the more symmetric cases. We show that very important features, such as the energy and the angular correlation of the emitted γ's, are characteristic effects of the emission from such deformed systems. For charge-asymmetric channels 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. (orig.)