Collective structure of the N = 40 isotones

The structure of even-even N=40 isotones is studied from drip line to drip line through the systematic investigation of their quadrupole modes of excitation. Calculations are performed within the Hartree-Fock-Bogoliubov approach using the Gogny D1S effective interaction. Where relevant, these calculations are extended beyond mean field within a generator-coordinate-based method. An overall good agreement with available experimental data is reported, showing that collectivity increases from the neutron to the proton drip line. Whereas {sup 60}Ca and {sup 68}Ni display a calculated spherical shape in their ground states, all other isotones show a prolate-deformed ground-state band and a quasi-{gamma} band. Coexistence features are predicted in the neutron-deficient N=40 isotones above {sup 74}Se.