[论文解读] Ferro-deformation and shape phase transitions over the nuclear chart: 50 < protons (Z) < 82 and 50 < neutrons (N) < 126

Chang-Bum Moon|arXiv (Cornell University)|Apr 4, 2016

Nuclear physics research studies参考文献 1被引用 5

一句话总结

本文提出了一种新型集体核形变现象——'铁-形变'（ferro-deformation），其由中子（h9/2）与质子（h11/2）在Z ≈ 64–66和N ≈ 102–104的原子核中强烈的同位旋依赖性自旋-轨道相互作用驱动。基于NNDC数据的E(2+)和R = E(4+)/E(2+)系统性分析，发现R = 3.3的饱和强化形变，标志出与伪壳层闭合及稀土与 actinide 核素中形变共存相关的临界形变相变。

ABSTRACT

We study a global nuclear structure in the framework of experimental observables. With the aid of large nuclear structure data at the national nuclear data center, NNDC, we present the distinctive systematic patterns emerged in the first 2+ excited energies, E(2+) and their energy ratios to the first 4+ levels, R = E(4+)/E(2+), in the even-even nuclei, over 50 < Z < 82 for protons, and 50 < N < 126 for neutrons. We introduce the so-called pseudo-shell configurations from the subshells mixture in order to explain a semi-double shell closure, a shape phase transition, and a reinforced deformation. It is found that the reinforced deformation arises when Z = 64 or 66 correlates with N = 90 and reaches its maximum, indicating R = 3.3. Such a saturated reinforced deformation spans over Z = 58 to 72 and N = 100 to 106 as showing its center at Z = 64 or 66 and at N = 102 or 104. We define this reinforced deformation 'a ferro-deformation' like a ferro-magnetism in condensed matter physics. The shape coexistence would be expected to occur, such as a ferro-deformation, with a strong rotational mode, and a near spherical shape, with a vibrational mode, at the critical points of Z = 64 or 66, with N = 88 and 90; 150Sm and 152Sm, 152Gd and 154Gd, and 154Dy and 156Dy. We suggest that a super-deformation, which can be formed at high-lying excited states in a moderate deformed nucleus, would correspond to the ferro-deformation at N = 88 for the nuclei; Sm, Gd, and Dy. We argue that the ferro-deformation can be closely associated with a strong spin-orbital interaction between neutrons and protons in the spin-orbit doublet, h9/2-h11/2, leading to the critical points at Z, N = 64, 104.

研究动机与目标

• 识别在50 ≤ Z ≤ 82和50 ≤ N ≤ 126范围内所有偶-偶核中低激发2+和4+能级的系统性规律。
• 通过亚壳层混合形成的伪壳层构型，解释强化形变和形变相变的出现机制。
• 提出'铁-形变'作为铁磁性的核物理类比，其由强同位旋依赖性自旋-轨道相互作用驱动。
• 预测在N = 88–90临界点处，如150Sm、152Gd和154Dy等核素中存在形变共存与超形变。

提出的方法

• 对50 ≤ Z ≤ 82和50 ≤ N ≤ 126范围内偶-偶核的实验E(2+)和R = E(4+)/E(2+)值进行系统性分析，数据来源为美国国家核数据中心（NNDC）。
• 引入由亚壳层混合形成的伪壳层构型，以解释半双壳层闭合与形变增强现象。
• 通过R = 3.3识别Z = 64/66和N = 104/102处的临界点，表明最大强化形变。
• 利用围绕N = 82对称的同质素对之间E(2+)能级差ΔE(2+)，探测中子与质子配对贡献。
• 分析ΔR值以评估集体振动与转动行为。
• 将观测到的形变模式与h9/2（中子）和h11/2（质子）轨道（l = 5）中同位旋依赖性自旋-轨道相互作用联系起来。

实验结果

研究问题

• RQ1 在50 ≤ Z ≤ 82和50 ≤ N ≤ 126的核素图上，E(2+)和R = E(4+)/E(2+)的系统性规律是什么？
• RQ2 由亚壳层混合形成的伪壳层构型如何解释观测到的强化形变与形变相变？
• RQ3 νh9/2与πh11/2轨道之间同位旋依赖性自旋-轨道相互作用在驱动铁-形变现象中起什么作用？
• RQ4 形变共存发生的位置与机制是什么，特别是在Z = 64/66和N = 88/90处？
• RQ5 铁-形变概念如何与中等形变核素高激发态中的超形变相关联？

主要发现

• 在Z = 64或66和N = 102或104为中心的核素中，观测到R = E(4+)/E(2+) = 3.3的饱和强化形变，覆盖Z = 58–72和N = 100–106的范围。
• 该现象被称为'铁-形变'，因其与铁磁性的类比，表明在核素图大范围内集体自由度的相干对齐。
• 在临界点Z = 64/66和N = 88/90预测存在形变共存，包括150Sm/152Sm、152Gd/154Gd和154Dy/156Dy，其中存在旋转与振动模式共存。
• 在Sm、Gd和Dy等中等形变核素的高激发能区观测到的超形变，被识别为N = 88时铁-形变的体现。
• νh9/2与πh11/2轨道（l = 5）之间同位旋依赖性自旋-轨道相互作用被确定为突然且剧烈形变变化及铁-形变起始的驱动力。
• 在Ba核素中未发现N = 88至90之间相变的证据，且140Sn（N = 90）被预测具有与邻近核素相似的结构特性，与壳层闭合效应的预期相反。