The equilibration of macroscopic degrees of freedom during the fusion of heavy nuclei,
like the charge and the shape, are studied in the Time-Dependent Hartree-Fock theory.
The pre-equilibrium Giant Dipole Resonance (GDR) is used to probe the fusion path.
It is shown that such isovector collective state is excited in N/Z asymmetric fusion and to a less extent
in mass asymmetric systems. The characteristics of this GDR are
governed by the structure of the fused system in its pre-equilibrium phase,
like its deformation, rotation and vibration.
In particular, we show that a lowering of the pre-equilibrium GDR energy is expected as compared
to the statistical one.
Revisiting experimental data, we extract an evidence of this lowering for the first time.
We also quantify
the fusion-evaporation enhancement due to gamma-ray emission from the pre-equilibrium GDR.
This cooling mechanism along the fusion path may be suitable to synthesize in the future
super heavy elements using radioactive beams with
strong N/Z asymmetries in the entrance channel. |
