1.School of Intelligent Manufacturing, Zhejiang Guangsha Vocational and Technical University of Construction, Zhejiang, Jinhua 322100, China 2.Institute of Nuclear Energy Safety Technology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Anhui, Hefei 230031, China 3.School of Electronic, Electrical Engineering and Physics, Fujian University of Technology, Fujian, Fuzhou 350118, China 4.Key Laboratory of High Precision Nuclear Spectroscopy, Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China 5.School of Physics, Zhengzhou University, Zhengzhou 450001, China 6.School of Physics, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand 7.Thailand Center of Excellence in Physics (ThEP), Commission on Higher Education, Bangkok 10400, Thailand 8.Division of Health Sciences, Hangzhou Normal University, Zhejiang, Hangzhou 310012, China 9.Department of Basic Sciences, Army Academy of Artillery and Air Defense, Anhui, Hefei 230031, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 11065001) and the Key Laboratory of High Precision Nuclear Spectroscopy, Institute of Modern Physics, Chinese Academy of Sciences
Received Date:26 January 2021
Accepted Date:21 May 2021
Available Online:18 September 2021
Published Online:05 October 2021
Abstract:Evidence for nonaxial γ deformations has been widely found in collective rotational states. The γ deformation has led to very interesting characteristics of nuclear motions, such as wobbling, chiral band, and signature inversion in rotational states. There is an interesting question; why the nonaxial γ deformation is not favored in the ground states of even-even (e-e) nuclei. The quest for stable triaxial shapes in the ground states of e-e nuclei, with a maximum triaxial deformation of $ \left| \gamma \right| $ ≈ 30°, is still a major theme in nuclear structure. In the present work, we use the cranked Woods-Saxon (WS) shell model to investigate possible triaxial shapes in ground and collective rotational states. Total-Routhian-surface calculations by means of the pairing-deformation-frequency self-consistent cranked shell model are carried out for even-even germanium and selenium isotopes, in order to search for possible triaxial deformations of nuclear states. Calculations are performed in the lattice of quadrupole (β2, γ) deformations with the hexadecapole β4 variation. In fact, at each grid point of the quadrupole deformation (β2, γ) lattice, the calculated energy is minimized with respect to the hexadecapole deformation β4. The shape phase transition from triaxial shape in 64Ge, oblate shape in 66Ge, again through triaxiality, to prolate deformations is found in germanium isotopes. In general, the Ge and Se isotopes have γ-soft shapes, resulting in significant dynamical triaxial effect. There is no evidence in the calculations pointing toward rigid triaxiality in ground states. The triaxiality of $ \gamma = - 30^\circ $ for the ground and collective rotational states, that is the limit of triaxial shape, is found in 64, 74Ge. One should also note that the depth of the triaxial minimum increases with rotational frequency increasing in these two nuclei. The present work focuses on the possible triaxial deformation of N = Z nucleus 64Ge. Single-particle level diagrams can give a further understanding of the origin of the triaxiality. Based on the information about single-particle levels obtained with the phenomenological Woods-Saxon (WS) potential, the mechanism of triaxial deformation in N = Z nucleus 64Ge is discussed, and caused surely by a deformed γ≈30° shell gap at Z(N) = 32. At N = 34, however, an oblate shell gap appears, which results in an oblate shape in 66Ge (N = 34). With neutron number increasing, the effect from the N = 34 oblate gap decreases, and hence the deformations of heavier Ge isotopes change toward the triaxiality (or prolate). Keywords:triaxial deformation/ total Routhian surface/ shape evaluation
图 1 总转动能面计算得出的偶质量核64-80Ge的基态形变. 误差棒显示对应于能量高出最小值100 keV以内的形变值, 此表示各个核对应于相应形变参数(
图 2 对64Ge的正宇称转晕态在给定转动频率 (a)
图 3 对应于三轴形变参数γ的Woods-Saxon势单粒子能级图
图 4 对(a) 74Ge和(b) 74Se核由TRS计算得到的运动学转动惯量J(1)与由实验结果提取出的比较
