M. Waroquier

We study the U(5), SU(3), SU∗(3) and O(6) limits of the neutron-proton interacting boson model. A group theoretical interpretation of the Majorana term is discussed. The B(M1;01+→11+) values are calculated in the four limits and in differen t classes of translational nuclei.

A “universal” effective NN interaction of the Skyrme type has been proposed which is suitable for both ground and excited states in nuclei throughout the nuclear mass table. The analytical structure of the proposed interaction SkE is presented and discussed. The spin stability of the force is studied by deriving the corresponding Landau-Migdal interaction for uniform nuclear matter. An equivalent set of force parameters starting from a realistic interaction after application of the local-density approximation (LDA) and the density-matrix expansion (DME) is derived. The behavior of the SkE interaction in describing charge properties is extensively discussed by carrying out a detailed and elaborate study of nucleon and charge distributions in ⁵⁸Ni, the Ca and Pb isotopes.

According to the scission-point model, the probability for a particular fission event can be expressed in terms of the collective potential and the collective kinetic energy at the scission point. Two additional assumptions make the scission-point model an easily calculable model: the assumption of equal collective kinetic energies for constant distances d between the tips of the fragments, and the assumption that one is able to characterize the excitation energy of the fragments with a nuclear temperature T, independent of both the mass ratio and the charge ratio, and of the deformations of the fragments. It is pointed out that the latter assumption violates energy conservation. A modified, recursive procedure is proposed, resulting in an "energy conservation consistent" scission-point method. Mass and charge distributions for the fission of ²³⁵U and ²⁵²Cf compound systems have been calculated and compared with distributions following the "standard" scission-point method of Wilkins, Steinberg, and Chasman.
NUCLEAR REACTIONS Scission-point model. Collective potential and intrinsic excitation energy. Nuclear temperature T. Mass and charge distributions. Fission of ²³⁵U and ²⁵²C.