Abstract
We present Large Scale Shell Model calculations using the effective interaction LNPS, which reproduce nicely the experimental data available in the N=40 island of deformation. We deal as well with the triple (shape?) coexistence in the low energy spectrum of 68Ni, showing that the highly deformed band based upon the excited 0+ state at 2627 keV is in fact the doorway to the island. The onset of prolate quadrupole collectivity and shape coexistence in the heavy N=Z nuclei, is explained by means of the realizations of the pseudo plus quasi SU3 symmetry, with special emphasis on the shape mixing in the ground state of 72 Kr.
Highlights
Why do the quadrupole correlations thrive in the nucleus? The fact that the spherical nuclear mean field is close to the harmonic oscillator has profound consequences, because its dynamical symmetry, responsible for the accidental degeneracies of its eigenvalues, is SU(3), which has among its generators the quadrupole operator
Our Large Scale Shell Model (LSSM) calculations in the valence space of the full pf -shell for the protons and the 0f5/2 1p3/2 1p1/2 0g9/2 and 1d5/2 orbits for the neutrons, predict another region of deformation centered in 64Cr
The onset of the different modes of quadrupole collectivity depend on the structure of the spherical mean field
Summary
Why do the quadrupole correlations thrive in the nucleus? The fact that the spherical nuclear mean field is close to the harmonic oscillator has profound consequences, because its dynamical symmetry, responsible for the accidental degeneracies of its eigenvalues, is SU(3), which has among its generators the quadrupole operator. This state is dominated by 2p-2h neutron excitations and is mildly oblate according to the calculations. The neutron 4p-4h configuration takes full advantage of the quadruple correlations (quasi-SU3 for the particles and pseudo-SU3 for the holes) if the corresponding proton configuration is a 2p-2h across Z=28, as it is the case in the calculations, because the two protons excited are in a pseudo-SU3 configuration as well.
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