**Quantum
microscopic calculations to heavy-ion fusion and quasi-fission**

Cedric
Simenel

CEA/IRFU/SPhN, France

The
fusion between two heavy ions is a complex, highly non linear,
and irreversible process. It
is strongly coupled to internal structures of the colliding
partners resulting from their quantum nature. Moreover the path to
fusion strongly depends on the mass of the nuclei. For instance, two light
nuclei in contact are likely to fuse, whereas this condition is
clearly not sufficient for heavy systems which exhibit a fusion
hindrance due to the quasi-fission mechanism. Indeed, in the
latter, a mass flow between the reactants occurs, leading to a
re-separation of more symmetric fragments in the exit channel. A good understanding of
the competition between fusion and quasi-fission mechanisms is
expected to be of great help to optimize the formation and study
of heavy and superheavy nuclei.

Modern
quantum microscopic models allow for a treatment of all degrees
of freedom associated to the dynamics of each nucleon in non
relativistic heavy-ion collisions. This provides a
description of the complex reaction mechanisms with no parameter
adjusted on reaction mechanisms. Such
approaches can then be used to describe various reaction
mechanisms with reaction partners spanning the entire nuclear
chart.

To
keep the amount of work for the physicist and his computer to a
reasonable level, approximations are considered rather than
solving the full Schrödinger equation. The choice of the
approximation depends on the particular type of observable of
interest. The
Balian-Vénéroni variational principle [1] provides
a useful starting point to derive various approximations to the
quantum dynamics. For example, expectation values of one-body
operators, like the evolution of the nuclear density, are
computed using the time-dependent Hartree-Fock (TDHF) theory. The latter assumes a
motion of independent particles in the mean-field generated by
the ensemble of particles. For
the fluctuation of one-body operators, however, we need to
include some correlations by solving an equation equivalent to
the time-dependent RPA. The
range of applications of these approaches is quite large, from
sub-barrier heavy-ion reactions [2] to more violent
deep-inelastic collisions [3].

The present
microscopic calculations are applied to nuclear collision around
the barrier, starting from light-medium systems to heavier
systems showing fusion hindrance. The quasi-fission
mechanism is investigated and compared to recent experimental
data.

[1]
R. Balian and M. Vénéroni, Phys. Lett. B **136**, 301 (1984).

[2]
C. Simenel, Phys. Rev. Lett. **105**, 192701 (2010).

[3]
C. Simenel, Phys. Rev. Lett. **106**, 112502 (2011).