Skyrme density functional description of the double magic Ni78 nucleus

Abstract

We calculate the single particle spectrum of the double magic nucleus 78 Ni in a Hartree-Fock approach using the Skyrme density-dependent effective interaction containing central, spin-orbit and tensor parts. We show that the tensor part has an important effect on the spin-orbit splitting of the proton 1f orbit which may explain the survival of magicity so far from the stability valley.We confirm the inversion of the 1f 5/2 and 2p3/2 levels at the neutron number 48 in the Ni isotopic chain expected from previous Monte Carlo shell model calculations and supported by experimental observation. *

The N=50 and Z=28 shell closure revisited

“…The nice agreement between both results points out, in agreement with Ref. [15], that the main effects of the tensor interaction can be very well reproduced by using a zero-range tensor force similar to that associated to the Skyrme forces [13]. It should be pointed out that when the tensor force is added in the QLDFT functional the parameters of the interaction should be readjusted.…”

“…There is not much experimental information available concerning the neutron single-particle levels in neutronrich Ni isotopes between 68 Ni and 78 Ni [15]. The SEI predicts that the gap between the 1g 9/2 and 2d 5/2 neutron levels remains practically constant for all the neutronrich isotopes considered, pointing out that the SEI model maintains the magic character of the neutron number N =50.…”

“…The predictions of the HF+BCS calculation using the D1MTd parametrization are compared in the lower panel of Fig. 2 with those provided by the QLDFT with D1M supplemented by a zero-range tensor force with parameters α T =−52.08 MeV fm 5 and β T =215.83 MeV fm 5 (see [15,20] for the definition of these parameters). The tensor term used for the D1MTd interaction has been defined as:…”

“…The question raised on the validity of the use of the zero-range tensor force in Ref. [14] is clarified later on in the recent work by Brink and Stancu [15], where they have shown that the momentum dependence of the zero-range tensor force [13] simulates the same effect as the finite-range tensor in- Solid: SLy5 [18] Dashed: SAMi-T [16] FIG.…”

“…teraction. With Skyrme forces, the use of a tensor term seems unavoidable to reproduce the position of the 2p 3/2 and 1f 5/2 single-particle proton levels in the Ni isotopic chain beyond neutron number N =40 [15] observed experimentally in Refs. [2,4,5,7] and interpreted theoretically with Monte-Carlo shell model calculations [8,9].…”