Collective Modes: Dynamical Dipole Excitation In Dissipative Heavy-Ion Reactions

The existence of the dynamical dipole mode in the Pb-192 composite system was investigated, through the study of its prompt gamma decay, employing the Ca-40 + Sm-152 and Ca-48 + Sm-144 reactions at E-lab=11 and 10.1 MeV/nucleon, respectively. The gamma-rays and light charged particles were detected in coincidence with evaporation residues and fission fragments. First results of this experiment show that the dynamical dipole mode survives in collisions involving heavier mass reaction partners than those studied previously. As a fast cooling mechanism on the fusion path, the prompt dipole gamma radiation could be of interest for the synthesis of super-heavy elements through "hot" fusion reactions. Furthermore, by using radioactive beams and the prompt gamma radiation as a probe we could get information on the symmetry energy at sub-saturation densities.