Relativistic mean field study of “island of inversion” in neutron-rich Ne, Na, Mg nuclei

Shape coexistence and the effective nucleon-nucleon interaction

“…Groundstate deformations in this mass region can also explain an anomalous isotope shift in 31 Na [17] and a major decrease in S 2n in 31,33,35 Na and 30 Ne [17,16]. The large deformation of 32 Mg has been inferred from the intermediateenergy Coulomb excitation studies [18].…”

“…In the shell-model language, the structural changes around 32 Mg can be attributed to the cross-shell particlehole excitations to the f 7/2 shell. Early shell-model calculations in a rather restricted configuration space (no more than two neutrons in the f 7/2 shell) [22] were able to reproduce the increased quadrupole collectivity at N =20.…”

“…In many calculations based on the mean-field theory, deformed ground states have been predicted in nuclei from the 32 Mg region (sometimes dubbed as an "island of inversion"). In the early Skyrme-HF calculations of Ref.…”

“…In the early Skyrme-HF calculations of Ref. [10] with the SIII and SIV interactions, large prolate deformations in 31,32 Na were obtained and explained in terms of neutron excitations from the sd shell to the f 7/2 shell. Similarly, low-lying 2 + states have been predicted in N =20 nuclei based on the energy density formalism [19].…”

“…For instance, the neutrondeficient Hg isotopes have well-deformed prolate ground states containing the high-j proton orbitals "intruding" across the Z=82 gap while the ground states of heavier Hg isotopes are only weakly deformed and they can be associated with oblate shapes. Such crossings between coexisting structures are particularly interesting in light nuclei; they can give rise to the presence of deformed ground states in magic nuclei such as 32 Mg. For an extensive review of shape coexistence in light and heavy nuclei, we would like to refer the reader to Refs. [1,2].…”