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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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