We discuss the need of including tensor terms in the effective Gogny interaction used in meanfield calculations. We show in one illustrative case that, with the usual tensor term that is employed in the Skyrme interaction (and that allows us to separate the like-nucleon and the neutron-proton tensor contributions), we can describe the evolution of the N = 28 neutron gap in calcium isotopes.We propose to include a tensor and a tensor-isospin term in finite-range interactions of Gogny type. The parameters of the two tensor terms allow us to treat separately the like-nucleon and the neutron-proton contributions. Two parameterizations of the tensor terms have been chosen to reproduce different neutron single-particle properties in the 48 Ca nucleus and the energy of the first 0 − state in the 16 O nucleus. By employing these two parameterizations we analyze the evolution of the N = 14, 28, and 90 neutron energy gaps in oxygen, calcium and tin isotopes, respectively.We show that the combination of the parameters governing the like-nucleon contribution is crucial to correctly reproduce the experimental (where available) or shell-model trends for the evolution of the three neutron gaps under study.
We present a study of the effects of the tensor-isospin term of the effective interaction in Hartree-Fock and random-phase approximation calculations. We used finite-range forces of Gogny type, and we added to them a tensor-isospin term which behaves, at large internucleonic distances, as the analogous term of the microscopic interactions. The strength of this tensor force has been chosen to reproduce the experimental energy of the lowest 0 − excited state in 16 O, which shows large sensitivity to this term of the interaction. With these finite-range interactions, we have studied the effects of the tensor-isospin force in ground and excited states of carbon, oxygen, calcium, nickel, zirconium, tin, and lead isotopes. Our results show that the tensor force affects mainly the nucleon single-particle energies. However, we found some interesting cases where also bulk nuclear properties are sensitive to the tensor interaction.
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