U. Mosel

The two-center shell model

Abstract The two-center shell model is summarized: spin-orbit and l2 terms are included in the double-center oscillator. Various conditions for volume conservation during the deformation process are studied. The shell structure for symmetric break-up is established and potential energy surfaces for nuclear fission are calculated.

Potential energy surfaces for heavy nuclei in the two-center model

Abstract Potential energy surfaces have been calculated for heavy nuclei in the framework of the two-center model, which has here been extended to realistic nuclear shapes. These surfaces are shown in a two-dimensional representation as a function of two parameters, one of which is a measure of the elongation of the nuclear shape and the other a measure of its constriction. The surfaces are discussed in comparison with other theoretical results and experimental information. Finally the influence of fragment shells on the potential energy surface is investigated. It is found that this influence is important already at early stages of the fission process.

Fission properties of heavy and superheavy nuclei

Abstract Calculations have been carried out to estimate the total fragment kinetic energies EK, total fragment excitation energies Ex, and approximate total number of neutrons ν emitted in the binary fission of heavy and superheavy nuclei. The kinetic energy calculations are based on a static scission model reported earlier for fissioning nuclei in the actinide region. The total energy release Q is calculated from a recent mass formula of Seeger, and the total excitation energy is obtained from the difference, Ex = Q − EK. The results show a strong peak in EK(A)[A = compound nucleus mass number] and a corresponding minimum in Ex(A), at A ≈ 264, corresponding to fission into two nearly double-magic (Z ≈ 50, N ≈ 82) fragments. Our predictions of EK, Ex, and ν disagree sharply with the liquid-drop predictions in the range 255 ⪅ A ⪅ 290. It appears from these results that kinetic energy measurements do not provide an unambiguous test for superheavy nuclei, while measurements of ν, if ν ⪆ 5 , seem to provide such a test.

Nuclear deformation energy in the two-center shell model☆

Abstract The two-center single-particle shell model is applied to the calculation of deformation energies and fission barriers of 236 U. The condition of volime conservation is used in three different ways and the results of the pure single-particle calculation are compared to those obtained with Strutinskys renormalization method.

Dipole excitations in fission fragments

Abstract Dipole excitations in fission fragments at the scission point have been studied in a classical model. These excitations correspond to a density fluctuation caused by the Coulomb repulsion between the fragments. A simple two-sphere approximation to the scission configuration is used for these studies. The dipole density distribution is obtained from a hydrodynamic picture of the fragment nucleus and the dipole amplitude parameters are fixed by minimizing the total potential energy at the scission point. Calculations have been made for the symmetric and asymmetric scission configurations corresponding to the fission of 235 U by thermal neutrons. The dipole excitation energy is found to be about 0.5 MeV in one fragment and at the same time, the total energy is lowered by 1 MeV from its value calculated with a uniform density distribution.