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 ${}^{60}\mathrm{Ca}$ and ${}^{68}\mathrm{Ni}$ 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 ${}^{74}\mathrm{Se}$.

• Received 6 October 2009

DOI:https://doi.org/10.1103/PhysRevC.80.064313