Recent experiments performed in neutron-rich copper isotopes have revealed a crossing in the nucleus 75 Cu between the 3/2 − and 5/2 − levels, which correspond to the ground state and the first excited state in isotopes with mass number below A = 75. Due to the strong single-particle character of these states, this scenario can be investigated through the analysis of the proton spectrum provided by mean-field models in nickel isotopes with neutron numbers between N = 40 and N = 50. In this work, we show that the aforementioned crossing is mainly driven by the mean field provided by the effective nucleon-nucleon and spin-orbit interactions. We also analyze the impact of the tensor interaction and find that in some mean-field models it is essential to reproduce the crossing of the 2p 3/2 and 1 f 5/2 proton single-particle levels, as in the case of the SAMi-T Skyrme force and the D1M Gogny interaction, whereas in other cases, as for example the SLy5 Skyrme force, a reasonable tensor force appears to be unable to modify the mean-field enough to reproduce this level crossing. Finally, in the calculations performed with the so-called simple effective interaction (SEI), it is shown that the experimental data in nickel and copper isotopes considered in this work can be explained satisfactorily without any explicit consideration of the tensor interaction.

An existing parametrization of the simple effective interaction (SEI) that is able to reproduce the experimentally known crossing between the 2p 3/2 and 1 f 5/2 single-particle (s.p.) proton levels in neutron-rich Ni isotopes has been generalized. We have added a short-range tensor force in order to describe the observed gaps between the 1h 11/2 and 1g 7/2 s.p. proton levels in the Sn isotopic chain and between the 1i 13/2 and 1h 9/2 s.p. neutron levels in N = 82 isotones without compromising the good agreement with the splittings in the Ni isotopes. Different scenarios where tensor effects are relevant are considered with the new interaction and its predictions are compared with results from other mean-field models and experimental data where available.

No abstract

Recent experiments performed in neutron-rich copper isotopes have revealed a crossing in the nucleus 75 Cu between the 3/2 − and 5/2 − levels, which correspond to the ground-state and the first excited state in isotopes with mass number below A = 75. Due to the strong single-particle character of these states, this scenario can be investigated through the analysis of the proton spectrum provided by mean-field models in nickel isotopes with neutron numbers between N =40 and N =50. In this work we show that the aforementioned crossing is mainly driven by the mean-field provided by the effective nucleon-nucleon and spin-orbit interactions. We also analyze the impact of the tensor interaction, and find that in some mean-field models it is essential to reproduce the crossing of the 2p 3/2 and 1f 5/2 proton single-particle levels, as in the case of the SAMi-T Skyrme force and the D1M Gogny interaction, whereas in other cases, as for example the SLy5 Skyrme force, a reasonable tensor force appears to be unable to modify the mean-field enough to reproduce this level crossing. Finally, in the calculations performed with the so-called simple effective interaction (SEI), it is shown that the experimental data in nickel and copper isotopes considered in this work can be explained satisfactorily without any explicit consideration of the tensor interaction.