Energy Density Functional analysis of shape evolution in N=28 isotones

Abstract

The structure of low-energy collective states in proton-deficient N=28 isotones is analyzed using structure models based on the relativistic energy density functional DD-PC1. The relativistic Hartree-Bogoliubov model for triaxial nuclei is used to calculate binding energy maps in the $\beta$-$\gamma$ plane. The evolution of neutron and proton single-particle levels with quadrupole deformation, and the occurrence of gaps around the Fermi surface, provide a simple microscopic interpretation of the onset of deformation and shape coexistence. Starting from self-consistent constrained energy surfaces calculated with the functional DD-PC1, a collective Hamiltonian for quadrupole vibrations and rotations is employed in the analysis of excitation spectra and transition rates of ${}^{46}$Ar, ${}^{44}$S, and ${}^{42}$Si. The results are compared to available data, and previous studies based either on the mean-field approach or large-scale shell-model calculations. The present study is particularly focused on ${}^{44}$S, for which data have recently been reported that indicate pronounced shape coexistence.

31 pages, 11 figures. arXiv admin note: text overlap with arXiv:1102.4193

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• Microscopic core-quasiparticle coupling model for spectroscopy of odd-mass nuclei
• Covariant density functional analysis of shape evolution in $N=40$ isotones
• Microscopic derivation of the Bohr-Mottelson collective Hamiltonian and its application to quadrupole shape dynamics
• Self-consistent collective coordinate for reaction path and inertial mass
• Low-lying 2${}^{+}$ states generated by $pn$-quadrupole correlation and $N=28$ shell quenching