Abstract
A peculiar phenomenon was observed experimentally in cold fission: the odd partition yields are favored over the even ones for excitations energies of the fragments smaller than 4 MeV. In this contribution, a microscopic model is proposed for the explanation of this odd-even effect in cold fission. This explanation is based on a mixing configuration mechanism that is produced during the fission process. This configuration mixing mechanism is obtained dynamically by solving a the generalized system of time-dependent pairing equations, which include a pair-breaking effect. The time dependent equations of motion for the pair breaking effect were corroborated with a condition that fixes dynamically the number of particles on the two fission fragment. The single particle level scheme was calculated with the Woods-Saxon superasymmetric two center shell model, providing a continuous variation of the single particle energies and of the wave functions from one nucleus up to two separated fragments. A first rule can be extracted from this model. The even-even fission products cannot be obtained at zero excitation energies because of the existence of dynamical excitations produced in the avoided- level-crossing regions when the nuclear system deforms slowly.
Highlights
A peculiar phenomenon was observed experimentally in cold fission: the odd partition yields are favored over the even ones for excitations energies of the fragments smaller than 4 MeV
The second situation can be obtained with an operator of the type αiα j that acts on a Bogoliubov wave function, two particles being obtained on the levels i and j
The total energy of the nuclear system is computed in the framework of the macroscopic-microscopic method [25, 26]
Summary
[10, 11]. This effect is linked to the important question of intrinsic excitation (quasiparticle excitations) during the dynamical evolution of the fissioning nucleus on ints way from ground state to scission. Another explanation can be based on the Landau-Zener promotion mechanism during fission [12] or at scission [13]
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