New effective interaction for f(5)pg(9)-shell nuclei

We present a new effective interaction for shell-model calculations in the model space consisting of the single-particle orbits 1 p 3 / 2 ,0 f 5 / 2 ,1 p 1 / 2 ,and0 g 9 / 2 . Starting with a realistic interaction based on the Bonn-C potential, 133 two-body matrix elements and four single-particle energies are modified empirically so as to fit 400 experimental energy data out of 69 nuclei with mass numbers A = 63 ∼ 96. The systematics of binding energies, electromagnetic moments and transitions, and low-lying energy levels are described. The soft Z = 28 closed core is observed, in contrast to the stable N = 50 shell closure. The new interaction is applied to systematic studies of three different chains of nuclei, Ge isotopes around N = 40, N = Z nuclei with A = 64 ∼ 70, and N = 49 odd-odd nuclei, focusing especially on the role of the g 9 / 2 orbit. The irregular behavior of the 0 + 2 state in Ge isotopes is understood as a result of detailed balance between the N = 40 single-particle energy gap and the collective effects. The development of the band structure in N = Z nuclei is interpreted in terms of successive excitations of nucleons into the g 9 / 2 orbit. The triaxial/ γ -soft structure in 64 Ge and the prolate/oblate shape coexistence in 68 Se are predicted, showing a good correspondence with the experimental data. The isomeric states in 66 As and 70 Brare obtained with the structure of an aligned proton-neutron pair in the g 9 / 2 orbit. Low-lying energy levels in N = 49 odd-odd nuclei can be classified as proton-neutron pair multiplets, implying that the obtained single-particle structure in this neutron-rich region appears to be appropriate. These results demonstrate that, in spite of the modest model space, the new interaction turns out to describe rather well properties related to the g 9 / 2 orbit in various cases, including moderately deformed nuclei.status: publishe