核能级密度的投影壳模型描述：偶偶核中的集体、对破裂及多准粒子区域
Projected shell model description of nuclear level density: Collective, pair-breaking, and multiquasiparticle regimes in even-even nuclei
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中文总结 AI 辅助
该研究提出一种新颖壳模型方法计算形变核的核能级密度，以$^{164}$Dy为例，划分NLD为集体、对破裂、多准粒子三个区域并分析其特征，还研究了NLD的宇称与角动量依赖。
中文摘要 AI 辅助
大量实验证据表明，激发态核主要由准粒子（qp）激发主导，这些准粒子形成的多体态包含来自不同轨道的核子对破裂。我们以这些多准粒子态作为壳模型基矢的构建块，提出一种新颖的壳模型方法来计算形变核的核能级密度（NLD）。包含两体剩余相互作用的壳模型对角化会产生大量具有确定角动量和宇称的本征态。我们证明，作为统计量的NLD对形变单粒子态的结构敏感依赖。作为该方法的首个实例，我们选取了一个形变程度高的稀土核$^{164}$Dy，其NLD已被Oslo方法广泛研究。通过与谱学测量得到的离散能级进行定量比较，我们发现：低能NLD曲线中显著的阶梯状结构可理解为集体激发和核子对破裂的结果；高能NLD中能级的指数增长可由受泡利原理约束的破裂对态组合来描述。根据随激发能增加的NLD特性，我们将整个NLD曲线划分为：（1）集体区域、（2）对破裂区域、（3）多准粒子区域。我们讨论了这三个区域NLD的形成机制和特征，并重点研究了NLD中的宇称依赖和角动量依赖及其结构效应。
英文摘要
There is overwhelmingly experimental evidence indicating that excited nuclear states are dominated by quasiparticle (qp) excitations, which form many-body configurations with broken nucleon-pairs from different orbitals. By using these multi-qp states as building blocks for a shell-model basis, we propose a novel shell-model method to calculate the nuclear level density (NLD) in deformed nuclei. The shell-model diagonalization with two-body residual interactions yields a large ensemble of eigenstates of angular momentum and parity. We demonstrate that NLD as a statistical quantity depends sensitively on the structure of deformed single-particle states. As the first example to introduce this method, we take a well-deformed rare-earth nucleus, $^{164}$Dy, for which NLD has been studied extensively by the Oslo method. By a quantitative comparison with discrete levels from spectroscopic measurements, we show that while the pronounced stepwise structure in the low-energy NLD curve can be understood as the collective excitation and nucleon-pair breaking, the exponential growth of levels in the higher-energy NLD can be described by the combination of the broken-pair states, subject to the Pauli principle. According to the nature of NLD with increasing excitation, we divide the entire NLD curve into (1) collective regime, (2) pair-breaking regime, and (3) multi-qp regime. We discuss the formation mechanism and characteristic features of NLD for the three regimes. In addition, the parity dependence and angular-momentum dependence in NLD are investigated with a strong emphasis on the structure effect.
