Effects of nuclear structure on quasi-fission

Cédric Simenel,D J Hinde,Aditya Wakhle,D H Luong,B Avez,M Dasgupta,R Du Rietz,M Evers,C J Lin

doi:10.1051/epjconf/20123809001

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

Introduction

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.

Fusion hindrance in heavy systems

Quasi-fission: interplay between shells and isospin

Quasi-fission within the TDHF approach

Findings

Conclusions and outlooks