[论文解读] Probing the two-quasiparticle $K^π=8^+$ isomeric structure and enhanced stability in the proton drip-line nuclei

Zhen-Zhen Zhang, Hua-Lei Wang+2 more|arXiv (Cornell University)|Jan 14, 2026

Nuclear physics research studies被引用 0

一句话总结

论文在质子排水线附近的160Os 84中，使用配置约束势面计算，研究两准粒子 Kπ=8⁺ 同位素在自旋轨道耦合和变形作用下的结构及可能的稳定性颠倒。

ABSTRACT

Stimulated by recent experimental discoveries [{Phys. Lett. B extbf{847}, 138310 (2023)} and {Phys. Rev. Lett. extbf{132}, 072502 (2024)}], two-quasiparticle $K^π=8^+$ isomeric structure (related to the neutron $h_{9/2}$ and $f_{7/2}$ orbitals) in $^{160}_{76}$Os$_{84}$ that lies at the two-proton drip line has been studied by means of the configuration-constrained potential-energy-surface calculations. Calculated results indicate that, for such an isomer, the excitation energy can be well reproduced and its oblate shape can be enhanced by the polarization effects of the two high-$K$ orbits. Comparing with experimental data, two sets of the widely used Woods-Saxon parameters, especially, the spin-orbit coupling one, are evaluated and argued. It is found that, considering the uncertainty of the spin-orbit coupling strength, the energy crossing or inversion of the $h_{9/2}$ and $f_{7/2}$ neutrons can occur, which may lead to three kinds of different evolution-trends of two-quasiparticle excitation energies with the changing quadrupole deformation $β_2$. With decreasing spin-orbit coupling interaction, the structure of the $K^π=8^+$ isomeric state will evolute from $νh_{9/2}f_{7/2}$ ($ν9/2^-[505] \otimes 7/2^-[503]$) to the mixing of $νh_{9/2}f_{7/2}$ and $νh_{9/2}^2$ ($ν9/2^-[505] \otimes 7/2^-[514]$) to $νh_{9/2}^2$, indicating that its structural probes is still of interest and an arbitrary assignment may be risky. The related theoretical calculations and experimental evidences e.g., the transition properties, are desirable. In addition, similar to that in superheavy nuclei, it is suggested that the stability inversion between high-$K$ isomeric states and ground states might occur in this proton drip-line mass region, e.g., in the hitherto unknown nucleus $^{162}_{78}$Pt$_{84}$.

研究动机与目标

• 研究160Os 84中两准粒子Kπ=8⁺同位素的本征结构及其由高-K 中子轨道驱动的扁椭圆形变。
• 评估自旋轨道耦合强度如何影响νh9/2和νf7/2中子轨道的相对排序以及同位素的构型。
• 评估在质子排水线N=84同位素（如162Pt 84）中，稳定性增强（同位素态vs基态）与潜在的稳定性颠倒。
• 在该局部质量区测试伍兹-桑笛平均场参数化（StkI 与 universal）及其对单粒子能级和同位素性质的影响。
• 探讨可能的实验观测量（如跃迁性质）以验证预测的结构。

提出的方法

• 在多维变形空间β2、γ、β4中的配置约束势面计算。
• 带变形伍兹-桑笛平均场和 Strutinsky 壳修正的宏观-显微能量。
• 带单极对偶配对的 Lipkin-Nagami 配对，以及用于多准粒子态的配置约束阻塞。
• 通过变形跟踪指定准粒子轨道的准粒子阻塞性；能量分解为变形分量和构型分量。
• 通过与146Gd和132Sn已知单粒子分裂比较来评估自旋轨道耦合强度不确定性，从而选择λ值（如 StkI 参数集）。
• 将计算的激发能量和变形与可用的实验数据（如8⁺同位素的E_ex）及早期理论进行比较。

Figure 1: Comparison between the available experimental data and the calculated single-particle energies in 146 Gd. Note that theoretical single-particle levels are solved by using the Woods-Saxon Hamiltonian with uni. and StkI model parameters, .

实验结果

研究问题

• RQ1 νh9/2–νf7/2 中子配置如何为160Os在质子排水线上的Kπ=8⁺同位素做出贡献？
• RQ2 同位素的激发能和变形对自旋轨道相互作用强度有多敏感？
• RQ3 在该质量区高-K扁椭圆同位素是否能表现出相对于基态的增强稳定性或颠倒？
• RQ4 伍兹-桑笛参数化（StkI 与 universal）是否能准确再现该原子核费米面附近的单粒子能级？
• RQ5 哪些实验观测量（如跃迁速率）可验证预测的同位素结构？

主要发现

• 160Os 的8⁺同位素的激发能约在1.84–1.89 MeV，具有扁椭圆形变（γ≈60°），并被来自高-K 轨道的极化效应增强。
• 自旋轨道耦合强度对νh9/2和νf7/2中子之间的相对排序具有决定性影响，可能导致穿越或颠倒，从而改变同位素的构型。
• 两组伍兹-桑笛参数（尤其是StkI）在局部区域对实验单粒子能量的拟合更好，影响同位素的预测。
• 计算表明基态变形呈弱扁椭圆，而高-K态通过阻塞高-j 轨道而稳定扁椭圆变形。
• 在质子排水线的同位素如162Pt 84中，高-K同位素态与基态之间存在潜在的稳定性颠倒情形，类似于超重核中的模式。
• 该研究强调需要跃迁性质数据以及进一步的实验/理论工作，以在自旋轨道不确定性下约束同位素结构。

Figure 2: Calculated single-particle energies near the Fermi surface for neutrons (similarly for protons) as functions of quadrupole deformation $\beta_{2}$ by using the Woods-Saxon Hamiltonian with the StkI (a) and universal (b) parameters Meng2018 ; Yang2016 ; Bhagwat2010 ; Bhagwat2023 for 160 Os.