Quadrupole collectivity in N≈28 nuclei with the angular momentum projected generator coordinate method

Properties of the ground and several collective excited states of selected neutron-rich $N=28$ isotones and sulfur isotopes around ⁴⁴S are described in the framework of the angular momentum projected generator coordinate method using the quadrupole moment as collective coordinate and the Gogny force, with the D1S parametrization, as the effective interaction. Fairly good agreement with available experimental data is obtained for the 2⁺ excitation energies and $B(E2)$ transition probabilities of the $N=28$ isotones. For the sulfur isotopes an acceptable agreement is found and the isotopic trend is well reproduced. It is found that the $N=28$ shell closure is not preserved in the prolate ⁴⁰Mg, the oblate deformed ⁴²Si, and the shape coexistent isotones ⁴⁴S and ⁴⁶Ar, whereas it is preserved (on the average) in ⁴⁸Ca. The sulfur isotopes ^38-42S are found to be, to some extent, prolate deformed.