Deformation of nuclei close to the two-neutron drip line in the Mg region

We present Hartree-Fock-Bogoliubov (HFB) calculations of the ground states of even Mg isotopes, A Skyrme force is used in the mean-field channel and a density-dependent zero-range force in the pairing channel. Mg-40 and Mg-20, are predicted to be at the two-neutron and two-proton drip lines respectively. A detailed study of the quadrupole deformation properties of all the isotopes shows that the ground stares of Mg-36,Mg-38,Mg-40 are strongly deformed with significantly different deformations for the neutrons and protons, Our study supports the disappearance of the N = 28 shell gap in the Mg and Si isotopes. (C) 1997 Elsevier Science B.V.