P. Sarriguren

Effective density-dependent pairing forces in the T=1 and T=0 channels

This work was supported by DGICYT-IN2P3 agreement and by DGICYT (Spain) under Contract No. PB95/0123.

Charge radii and structural evolution in Sr, Zr, and Mo isotopes

The evolution of the ground-state nuclear shapes in neutron-rich Sr, Zr, and Mo isotopes, including both even-even and odd-A nuclei, is studied within a self-consistent mean-field approximati on based on the D1S Gogny interaction. Neutron separation energies and charge radii are calculated and compared with available data. A correlation between a shape transition and a discontinuity in those observables is found microscopically. While in Sr and Zr isotopes the steep behavior observed in the isotopic dependence of the charge radii is a consequence of a sharp prolate-oblate tran sition, the smooth behavior found in Mo isotopes has its origin in an emergent region of triaxiality.

Shapes and beta decay in proton rich Ge, Se, Kr and Sr isotopes

Abstract We study ground states and β-decay properties of the proton rich isotope chains Ge, Se, Kr, and Sr. We use a deformed selfconsistent HF+RPA approach with density-dependent effective interactions of Skyrme type. We find that most of the isotopes present two HF minima corresponding to two different shapes. In addition to static quadrupole moments and other ground state band properties, we present results for Gamow Teller strength distributions, as well as for half-lives and summed strengths. The role of deformation is particularly emphasized.

Charge and matter distributions and form factors of light, medium, and heavy neutron-rich nuclei

Results of charge form factors calculations for several unstable neutron-rich isotopes of light, medium, and heavy nuclei (He, Li, Ni, Kr, Sn) are presented and compared to those of stable isotopes in the same isotopic chain. For the lighter isotopes (He and Li) the proton and neutron densities are obtained within a microscopic large-scale shell-model, while for heavier ones Ni, Kr, and Sn the densities are calculated in deformed self-consistent mean-field Skyrme HF+BCS method. We also compare proton densities to matter densities together with their rms radii and diffuseness parameter values. Whenever possible comparison of form factors, densities and rms radii with available experimental data is also performed. Calculations of form factors are carried out both in plane wave Born approximation (PWBA) and in distorted wave Born approximation (DWBA). These form factors are suggested as predictions for the future experiments on the electron-radioactive beam colliders where the effect of the neutron halo or skin on the proton distributions in exotic nuclei is planned to be studied and thereby the various theoretical models of exotic nuclei will be tested.

β decay and shape isomerism in 74Kr

Abstract We study the properties of 74 Kr, and particularly the Gamow-Teller strength distribution, using a deformed self-consistent HF+RPA method with Skyrme type interactions. Results are presented for two density-dependent effective two-body interactions, including the dependence on deformation of the HF energy that exhibits two minima at close energies and distant deformations, one prolate and one oblate. We study the role of deformation, residual interaction, pairing and RPA correlations on the Gamow-Teller strength distribution. Results on moments of inertia and gyromagnetic factors, as well as on E0 and M1 transitions are also presented.

Role of triaxiality in the ground state shape of neutron rich Yb, Hf, W, Os, and Pt isotopes

The evolution of the ground-state shape along the triaxial landscape of several isotopes of Yb, Hf, W, Os, and Pt is analyzed using the self-consistent Hartree- Fock-Bogoliubov approximation. Two well reputed interactions (Gogny D1S and Skyrme SLy4) have been used in the study in order to asses to which extent the results are independent of the details of the effective interaction. A large number of even-even nuclei, with neutron numbers from N = 110 up to N = 122 has been considered, covering in this way a vast extension of the nuclear landscape where signatures of oblate-prolate shape transitions have already manifested both theoretically and experimentally.

Deformed quasiparticle random phase approximation formalism for single- and two-neutrino double β decay

We use a deformed QRPA formalism to describe simultaneously the energy distributions of the single beta Gamow-Teller strength and the two-neutrino double beta decay matrix elements. Calculations are performed in a series of double beta decay partners with A = 48, 76, 82, 96, 100, 116, 128, 130, 136 and 150, using deformed Woods-Saxon potentials and deformed Skyrme Hartree-Fock mean fields. The formalism includes a quasiparticle deformed basis and residual spin-isospin forces in the particle-hole and particle-particle channels. We discuss the sensitivity of the parent and daughter Gamow-Teller strength distributions in single beta decay, as well as the sensitivity of the double beta decay matrix elements to the deformed mean field and to the residual interactions. Nuclear deformation is found to be a mechanism of suppression of the two-neutrino double beta decay. The double beta decay matrix elements are found to have maximum values for about equal deformations of parent and daughter nuclei. They decrease rapidly when differences in deformations increase. We remark the importance of a proper simultaneous description of both double beta decay and single Gamow-Teller strength distributions. Finally, we conclude that for further progress in the field it would be useful to improve and complete the experimental information on the studied Gamow-Teller strengths and nuclear deformations.

Spin-isospin excitations and beta(+)/EC half-lives of medium-mass deformed nuclei

Abstract A selfconsistent approach based on a deformed HF + BCS + QRPA method with density-dependent Skyrme forces is used to describe β + -decay properties in even–even deformed proton-rich nuclei. Residual spin–isospin forces are included in the particle–hole and particle–particle channels. The quasiparticle basis contains neutron–neutron and proton–proton pairing correlations in the BCS approach, while neutron–proton pairing interaction is treated as a residual force in QRPA. We discuss the sensitivity of Gamow–Teller strength distributions and β + / EC half-lives to deformation, pairing and the strength of the particle–particle interaction. The dependence on deformation is also compared to that of spin M1 strength distributions.

Mean field study of structural changes in Pt isotopes with the Gogny interaction

The evolution of the nuclear shapes along the triaxial landscape is studied in the Pt isotopic chain using the self-consistent Hartree-Fock-Bogoliubov approximation based on the Gogny interaction. In addition to the parametrization D1S, the new incarnations D1N and D1M of this force are also included in our analysis to assess to which extent the predictions are independent of details of the effective interaction. The considered range of neutron numbers 88 N 126 includes prolate, triaxial, oblate, and spherical ground-state shapes and serves as a detailed comparison of the predictions obtained with the new sets D1N and D1M against the ones provided by the standard parametrization Gogny-D1S in a region of the nuclear landscape for which experimental and theoretical fingerprints of shape transitions have been found. Structural evolution along the Pt chain is discussed in terms of the deformation dependence of single-particle energies.

Semi-classical treatment of proton–neutron monopole interaction

Abstract We apply a time dependent variational method to a many-body Hamiltonian consisting of a spherical shell model term, a proton–proton and neutron–neutron pairing interaction and a monopole particle–hole and particle–particle proton–neutron interaction. The variational state is a generalized BCS state where all T=1 Cooper pairs with T z =0,±1 are included. Stationary solutions correspond to generalized BCS equations and define the static ground state. The linearized equations of motion are of RPA type and describe small oscillations of the nuclear system around the static ground state. Numerical application is made for a one level case. In contrast to previous treatments, the proton–neutron particle–particle interaction is included first in the mean field equations, defining the quasiparticle approximation, and then the residual interaction is taken into account by the RPA approach. In this way one obtains a noncollapsing RPA ground state.