Abstract
The quasi-fission mechanism hinders fusion of heavy systems because of a mass flow between the reactants, 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. Quantum microscopic models, such as the time-dependent Hartree-Fock approach, allow for a treatment of all degrees of freedom associated to the dynamics of each nucleon. This provides a description of the complex reaction mechanisms, such as quasi-fission, with no parameter adjusted on reaction mechanisms. In particular, the role of the deformation and orientation of a heavy target, as well as the entrance channel magicity and isospin are investigated with theoretical and experimental approaches.
Highlights
The formation of the heaviest nuclei usually involves fusionevaporation reactions [1,2,3,4]. The latter are strongly hindered in the case of heavy ion reactions by two competing mechanisms: (i) the quasi-fission (QF) process, and (ii) the statistical fission of the compound nucleus (CN)
The two fragments re-separate with more mass symmetry than the entrance channel, without forming a compound nucleus
The quasi-fission process, which is responsible for the fusion hindrance in heavy system, strongly depends on the entrance channel properties
Summary
The formation of the heaviest nuclei usually involves fusionevaporation reactions [1,2,3,4]. The QF mechanism is responsible for the fusion hindrance observed in heavy systems [10] In these reactions, an additional energy above the Coulomb barrier, sometimes called ”extra-push” energy [11], is needed for the system to fuse and form a CN. The TDHF approach has been successful in describing several reaction mechanisms, such as fusion, nucleon transfer, and deep-inelastic collisions We discuss results of a recent study of quasi-fission with TDHF calculations.
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