Collective modes: dynamical dipole excitation in dissipative heavy-ion reactions
D. Pierroutsakou 1*
1 INFN Section of Naples
An experimental overview [1-6] on the dynamical
dipole mode, excited in charge asymmetric dissipative
heavy-ion collisions, will be presented. In a campaign of
experiments where the same compound nucleus, in the
132Ce mass region, was probed through different charge
asymmetry entrance channels, a larger
gamma-ray emission in
the Giant Dipole Resonance energy range was evidenced
for the more charge asymmetric channel. This extra gamma
yield was related to the dynamical dipole mode decay. Its
angular distribution, studied at Elab = 16 MeV/nucleon,
supports its prompt dynamical nature [4, 5] while its
beam energy dependence presents a maximum at Elab=
9 MeV/nucleon [2-5]. The data [2-5] are compared with
theoretical calculations performed within a BNV transport
model and based on a collective bremsstrahlung
analysis of the entrance channel reaction dynamics .
The dynamical dipole mode could be considered as
a fast cooling mechanism of the composite system
that might favor the synthesis of super-heavy elements
through hot fusion reactions. However, its yield is predicted
to decrease in collisions involving heavier mass
partners . To shed light in this direction and to study
if pre-equilibrium eects survive in heavier systems, we
searched for the dynamical dipole mode in the 192Pb
compound nucleus by employing the 40 Ca+152 Sm and
48 Ca+144 Sm fusion-evaporation and fission reactions at
Elab =440 MeV and 485 MeV, respectively.
Using the prompt dipole radiation as a probe and employing
radioactive beams, new possibilities for the investigation
of the symmetry energy at sub-saturation density
are foreseen  and will be discussed.
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