The Study of the N=28 shell closure : a way to probe nuclear forces

The present contribution focuses on few recent experimental achievements related to the study of the N = 28 shell closure south to the doubly magic nucleus Ca-48(20). It is shown that a gradual change from spherical to deformation occurs in the N = 28 isotones from Z = 20 to Z = 14. This feature is ascribed to specific proton-neutron interactions, such as tensor forces, and to the posibility to develop quadrupole correlations between the occupied and valence states.