The three shapes of

The N=20 and N=28 “islands of inversion” are described by large scale shell model calculations which mix configurations with different Nħω or equivalently with different number of particles promoted from the sd-shell to the pf -shell. We pay particular attention to the properties of the states at fix Nħω which turn out to be the real protagonists of the physics at N=20. In particular we study the appearance of spherical, deformed and superdeformed structures in 32Mg at fixed 0p-0h, 2p-2h and 4p-4h configurations. Finally we submit that the islands of deformation at N=20 and N=28 merge in the Magnesium isotope