Particle-core coupling around 68Ni: a study of the subshell closure at N=40

The existence of a subshell gap at neutron number N=40 is investigated in the odd-mass Ni and Cu isotopes using the Particle-Core Coupling Model (PCM). The calculated properties are in good agreement with the existing experimental data, suggesting that 68Ni is a good core for the adjacent nuclei. Evaluation of the 2+1 excitation energies, two-neutron separation energies, and pairing properties of the Ni isotopes reveals discontinuities at neutron number N=40. These data support the existence of a significant neutron subshell gap at N=40, for Z=28. The systematic behavior of the proton single-particle energies extracted from the particle-core coupling calculations for the odd-mass Cu isotopes is discussed in terms of monopole shifts. The effect is consistent with the existence of a neutron subshell gap at N=40