原子核中普遍存在的三轴形状与复合物体旋转的量子理论
Prevailing Triaxial Shapes in Atomic Nuclei and a Quantum Theory of Rotation of Composite Objects
AI总结：
本研究提出重变形核普遍具有三轴形状，指出其源于对称性恢复的结合能增益与核力特定分量的增益，通过组态相互作用计算验证，阐明了转动带结构并建立了不依赖经典刚体量子化的多体旋转量子理论。
摘要：
传统观点认为，重变形核类似于轴对称的长椭球体，绕其中一条短轴旋转。而在本研究的图景中，它们的形状可能是三轴的。三轴形状会产生复杂的旋转，这实际上能很好地重现实验数据，最新的Configuration Interaction（组态相互作用）计算已证实了这一点。研究提出了三轴性的两个来源：（i）通过三轴形状的对称性恢复获得的结合能增益，（ii）通过核力的特定分量（如张量力和高多极（例如十六极）中心力）获得的另一部分增益。来源（i）几乎为所有变形核产生基本的较小三轴性，而来源（ii）则为某一类核产生中等三轴性。前者的一个例子是¹⁵⁴Sm，它是轴对称性的典型展示案例，但现在被认为表现出适度但有限的三轴性。对于后者即中等三轴性，研究从多个角度讨论了包括¹⁶⁶Er在内的一些示例核以及相关实验发现。研究阐明了γ带和双γ带的多体结构。关于包括三轴系统在内的变形多体系统旋转态的一般特征，研究在量子力学多体理论框架内讨论了著名的旋转激发能J(J+1)定则，并未借助旋转经典刚体的量子化。由此出现了普遍三轴形状的图景：经验上已知的转动带模式以良好的K量子数呈现，但其内部结构与A. Bohr提出的传统图景不同。研究还提及了与Davydov刚性三轴转子模型的可能联系。
英文摘要：
In the traditional view, heavy deformed nuclei are like axially-symmetric prolate ellipsoids, rotating about one of the short axes. In the present picture, their shapes may be triaxial. The triaxial shape yields complex rotations, which actually well reproduce experimental data, as confirmed by state-of-the-art Configuration Interaction calculations. Two origins are suggested for the triaxiality: (i) binding-energy gain by the symmetry restoration for triaxial shapes, and (ii) another gain by specific components of the nuclear force, like tensor force and high-multipole (e.g. hexadecupole) central force. While the origin (i) produces basic smaller triaxiality for virtually all deformed nuclei, the origin (ii) produces medium triaxiality for a certain class of nuclei. An example of the former is 154Sm, a typical showcase of axial symmetry but is now suggested to depict a modest yet finite triaxiality. The latter, medium triaxiality, is discussed from various viewpoints for some exemplified nuclei including 166Er, and experimental findings. Many-body structures of the gamma band and the double-gamma band are clarified. Regarding the general features of rotational states of deformed many-body systems including triaxial ones, the well-known J(J+1) rule of rotational excitation energies is discussed, within the quantum mechanical many-body theory, without resorting to the quantization of a rotating classical rigid body. The picture of prevailing triaxial shapes thus emerges, where the empirically known rotational-band pattern appears with good K quantum number, but the internal structure is dfferent from conventional picture a la A. Bohr. The possible relations to Davydov's rigid-triaxial-rotor model are mentioned.
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