Study of charge-exchange excitations in doubly magic nuclei in a self-consistent HF plus RPA approach

Self consistren Hartree Fock plus Random Phase Approximation containig Spin-Orbit and Coulomb terms.

We investigate the effects of the pairing in spherical nuclei. We use the same finite-range interaction of Gogny type in the three steps of our approach, Hartree–Fock, Bardeen, Cooper, and Schrieffer, and quasiparticle random-phase-approximation calculations. We study electric- and magnetic-dipole and quadrupole and octupole excitations in oxygen and calcium isotopes and also in isotones with 20 neutrons. We investigate the pairing effects on single-particle energies and occupation probabilities, on the excitation energies, B values, and collectivity of low-lying states including the isoscalar electric-dipole and magnetic-dipole excitations, and also the giant resonances. The inclusion of the pairing increases the values of the excitation energies in all the cases that we have studied. In general, the effects of the pairing are too small to noticeably improve the agreement with the available experimental data.

The first applications of the second random-phase-approximation model with the finite-range Gogny interaction.

We present a technique that treats, without approximations, the continuum part of the excitation spectrum in random phase approximation calculations with finite-range interactions. The interaction used in Hartree- Fock calculations to generate the single-particle basis is also used in continuum random phase approximation calculations. We show results for electric dipole and quadrupole excitations in 16O, 22O, 24O, 40Ca, 48Ca, and 52Ca nuclei. We compare our results with those of the traditional discrete random phase approximation, with continuum independent-particle model results, and with results obtained by a phenomenological random phase approximation approach. We study the relevance of the continuum, of the residual interaction, and of the self-consistency. We also compare our results with the available total photoabsorption cross-section data.

Self-consistent calculations of charg-excitations in double magic nuclei.

Comparison betwee Hartree-Fock plus Bardeen-Cooper-Schrieffer and Hartree-Fock-Bogolioubov results

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 theN = 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 parametrizations of the tensor terms have been chosen to reproduce different neutron single-particle properties in the 48Ca nucleus and the energy of the first 0− state in the 16O nucleus. By employing these two parametrizations 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 16O, 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.