Effects of the tensor force on the ground state and first 2+ states of the magic 54Ca nucleus

Abstract

The magic nature of the Ca-54 nucleus is investigated in light of recent experimental results. We employ both Hartree-Fock-Bogoliubov and Hartree-Fock (HF)+BCS methods using Skyrme-type SLy5, SLy5+T, and T44 interactions. The evolution of the single-particle spectra is studied for the N = 34 isotones: Fe-60, Cr-58, Ti-56, and Ca-54. An increase is obtained in the neutron spin-orbit splittings of p and f states due to the effect of the tensor force which also makes Ca-54 a magic nucleus candidate. Quasiparticle random-phase approximation calculations on top of HF+BCS are performed to investigate the first J(pi) = 2(+) states of the calcium isotopic chain. A good agreement for excitation energies is obtained when we include the tensor force in the mean-field part of the calculations. The first 2(+) states indicate a subshell closure for both Ca-52 and Ca-54 nuclei. We confirm that the tensor part of the interaction is quite essential in explaining the neutron subshell closure in Ca-52 and Ca-54 nuclei.