Exotic break-up modes in heavy ion reactions at low energies

New reaction mechanisms occurring in heavy ion collisions at low energy (10- 30 MeV/A) are investigated within the Stochastic Mean Field model. We concentrate on the analysis of ternary breakup events, of dynamical origin, occurring in semi-central reactions, where the formation of excited systems in various conditions of shape and angular momentum is observed. We show how this fragmentation mode, which can be considered as a precursor of the neck emission observed at higher beam energies, emerges from the combined action of surface (neck) instabilities and angular momentum effects. Interesting perspectives are opening towards the investigation of this mechanism in neutron-rich (or exotic) systems, with the possibility to access information on the low-density behavior of the nuclear symmetry energy.

Symmetry Energy Effects on Fusion Cross Sections

We investigate the reaction path followed by Heavy Ion Collisions with exotic nuclear beams at low energies. We will focus on the interplay between reaction mechanisms, fusion vs. break-up (fast-fission, deep-inelastic), that in exotic systems is expected to be influenced by the symmetry energy term at densities around the normal value. The evolution of the system is described by a Stochastic Mean Field transport equation (SMF), where two parametrizations for the density dependence of symmetry energy (Asysoft and Asystiff) are implemented, allowing one to explore the sensitivity of the results to this ingredient of the nuclear interaction. The method described here, based on the event by event evolution of phase space quadrupole collective modes will nicely allow to extract the fusion probability at relatively early times, when the transport results are reliable. Fusion probabilities for reactions induced by 132Sn on 64,58Ni targets at 10 AMeV are evaluated. We obtain larger fusion cross sections for the more n-rich composite system, and, for a given reaction, in the Asysoft choice. Finally a collective charge equilibration mechanism (the Dynamical Dipole) is revealed in both fusion and break-up events, depending on the stiffness of the symmetry term just below saturation.

Inverse Cotton-Mouton effect of the Vacuum and of atomic systems

In this letter we calculate the Inverse Cotton-Mouton Effect (ICME) for the vacuum following the predictions of Quantum ElectroDynamics. We compare the value of this effect for the vacuum with the one expected for atomic systems. We finally show that ICME could be measured for the first time for noble gases using state-of-the-art laser systems and for the quantum vacuum with near-future laser facilities like ELI and HiPER, providing in particular a test of the nonlinear behaviour of quantum vacuum at intensities below the Schwinger limit of 4.5x10^33 W/m^2.