科研之友
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摘要
We present a new effective interaction for shell-model calculations in the model space consisting of the single-particle orbits 1p(3/2), 0f(5/2), 1p(1/2), and 0g(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 similar to 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 similar to 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/gamma-soft structure in Ge-64 and the prolate/oblate shape coexistence in Se-68 are predicted, showing a good correspondence with the experimental data. The isomeric states in As-66 and Br-70 are 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.
- 出版日期2009-12
