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对原子核形状共存和壳效应的研究有助于人们深入理解原子核内部结构。物理学家们在Zn，Ge，Se，Kr的同位素研究中，发现了显著的形状共存现象与刚性三轴性特征。为了深入探究形状共存现象及其对原子核基态性质的影响，我们采用相对论Hartree-Bogoliubov理论中密度依赖的介子交换模型，对N = 32-42的偶偶核Zn，Ge，Se，Kr同位素的基态性质进行了系统研究，获得的势能面清晰地展现了这些同位素存在形状共存和三轴性特征。计算获得了原子核的基态能量、形变参数、双中子分离能、中子半径、质子半径和电荷半径，结果都支持N = 40为新幻数,部分结果也支持N = 32、34为新幻数。尤其，三轴形变在其中扮演着重要角色。进一步，我们探讨了壳效应与形状共存现象之间可能存在的关联及其对原子核基态性质的影响，并分析了这些变化的物理机制。The atomic nucleus is an extremely complex quantum many-body system composed of nucleons, and its shape is determined by the number of nucleons and their interactions. The study of atomic nuclear shapes is one of the most fascinating topics in nuclear physics, providing rich insights into the microscopic details of nuclear structure. Physicists have observed significant shape coexistence phenomena and stable triaxial deformation in isotopes of Zn, Ge, Se, and Kr. This paper aims to delve deeper into the impact of shape coexistence and triaxiality on the ground-state properties of atomic nuclei, as well as to verify new magic numbers.
We employed the density-dependent meson-exchange model within the framework of the Relativistic Hartree-Bogoliubov (RHB) theory to systematically study the ground-state properties of even-even Zn, Ge, Se, and Kr isotopes with neutron numbers N=32-42. The calculated potential energy surfaces clearly demonstrate the presence of shape coexistence and triaxial characteristics in these isotopes. By analyzing the ground-state energy, deformation parameters, two-neutron separation energies, neutron radii, proton radii, and charge radii of the atomic nuclei, we discuss the closure of nuclear shells. Our results reveal that at N=32, there is a notable abrupt change in the two-neutron separation energies of 62Zn and 64Ge. At N=34, a significant decrease in the two-neutron separation energies of 68Se and 70Kr is observed, accompanied by an abrupt change in their charge radii. Meanwhile, at N=40, clear signs of shell closure are observed. the maximum specific binding energy may correlate with the emergence of spherical nuclear structures. The shell closure not only enhances nucleon binding energy but also suppresses nuclear deformation through symmetry constraints. Our findings support N=40 as a new magic number, and some results also suggest that N=32 and N=34 could be new magic numbers. Notably, triaxial deformation plays a crucial role here. Furthermore, we explore the potential correlation between triaxiality and shape coexistence on the ground-state properties of atomic nuclei and analyze the physical mechanisms underlying these changes.
The discrepancies between current theoretical predictions and experimental data reflect limitations in modeling higher-order many-body correlations (e.g., three-nucleon forces) and highlight challenges in experimental measurements for extreme nuclear regions (including neutron-rich and near-proton-drip-line regions). Future studies could combine tensor force corrections, large-scale shell model calculations, and high-precision data from next-generation radioactive beam facilities (e.g., FRIB, HIAF) to clarify the interplay among nuclear force parameterization, proton-neutron balance, and emergent symmetries, thereby providing a more comprehensive theoretical framework for nuclear structure under extreme conditions.-
Keywords:
- shape coexistence /
- shell effect /
- new magic numbers
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