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.
Highlights
In the low energy fission, the mass and charge distributions of fragments show a preference for even numbers of neutrons and protons [1,2,3,4,5]
In the case of cold fission, where the excitation energy of the fragments is so small that no neutrons can be emitted, an inversion of the oddeven effect is produced
This behavior is typical, being observed for the fission of Cf [9, 10]. This inversion can be explained statistically by involving the level densities of odd and even nuclei [11, 12]. This effect should be linked to the important problem of single particle excitations along the dynamical evolution of the nuclear system in a large scale collective amplitude motion
Summary
In the low energy fission, the mass and charge distributions of fragments show a preference for even numbers of neutrons and protons [1,2,3,4,5]. As evidenced experimentally [7, 8] for U isotopes, in the cold region regime the oddodd fragmentations dominate at excitations energies lower than 4–6 MeV. This behavior is typical, being observed for the fission of Cf [9, 10]. This inversion can be explained statistically by involving the level densities of odd and even nuclei [11, 12] This effect should be linked to the important problem of single particle excitations along the dynamical evolution of the nuclear system in a large scale collective amplitude motion. In principle, such excitations can be produced by the Landau-Zener promotion mechanism [13, 14]
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