Shell-model and deformed Hartree-Fock plus BCS calculations are reported for even-even nuclei ${}^{18-30}\mathrm{O},$ ${}^{18-36}\mathrm{Ne},$ and ${}^{20-42}\mathrm{Mg};$ shell-model calculations additionally included ${}^{38,40}\mathrm{Ne}$ and ${}^{44,46,48}\mathrm{Mg}.$ Ground-state binding energies and $2_1^{+}$ quadrupole moments are calculated by both models. Shell-model calculations, aided by a new truncation method, include $2_1^{+}$ excitation energies and magnetic moments. Hartree-Fock calculations with SkI6, RATP, $Z_{\sigma }^{*},$ and SkX Skyrme forces include ground-state deformations and rms radii; SkI6 gives the best overall agreement with experiment. The two models are compared with each other and with experiment. Two-neutron separation energies, evidence for a neutron halo or skin in heavy O isotopes, and deformation of Ne and Mg isotopes are discussed. Both models indicate disappearance of the shell gap at $N=28\mathrm{}$ (Mg), and the shell model does so additionally at $N=20\mathrm{}$ (Ne and Mg).

• Received 21 December 1998

DOI:https://doi.org/10.1103/PhysRevC.60.034312