Odd-even effect dependence on the excitation energy in low energy fission

Abstract

Abstract. An inversion of the odd-even effect was observed experimentally in cold fission: the odd-odd fragmentation yields are favored over the even-even ones for excitations energies of the fragments smaller than 4 MeV. This effect is linked to the important problem of quasiparticle excitations during the dynamical evolution of the nuclear system from its ground-state configuration up to scission. An explanation based on the Landau-Zener promotion mechanism generalized for superfluid systems is offered for the inversion of the odd-even effect. In principle, the even-even fission products cannot be produced at very low excitation energies due dynamical quasiparticle excitations produced in the avoided-level-crossing regions. These excitations are produced with a large probability when the nuclear system deforms slowly.

Theoretical description of fission yields: towards a fast and efficient global model

“…From a microscopic point of view, OES in charge yields can be related to the dynamical breaking of Cooper pairs in avoided-level-crossing regions, where the Landau-Zener effect results in low-lying time dependent excitations [9,10]. In an apparently uncorrelated manner, peak positions in fragment distributions are mainly governed by the shell effects determining the most probable fission configuration, which, within certain models, may be manifested through the topology of the collective potential energy surface (PES).…”