New Aspects of Nuclear Deformation

本课题从动态和静态两方面对核四极和八极变形进行了新的研究。我们使用的理论工具是相互作用玻色子模型（IBM）。已知质量数为-130的Xe和Ba核具有伽马不稳定变形，并由IBM的0(6)极限描述。在经典的术语中，O(6)极限被认为是一个伽马不稳定转子。然而，我们发现了另一种情况，其中O(6)极限的所有特征态都可以构造为多声子态。这种新方法被称为q -声子方案。声子在这个方案中被激发在一个变形平衡的顶部。这个方案在描述状态时看起来非常强大，甚至在0(6)极限之外。例如，除了奇异点之外，yrast奇自旋态可以描述为q声子态。从转动阻尼和宽度两个方面对量子混沌作了进一步的研究。我们得到了宽度的合理估计，并讨论了分支数等问题。研究了八极子的变形，特别注意了电偶极子的跃迁。用相互作用玻色子-费米子模型-2分析了偶偶Pd同位素和奇a稀土核的g因子和M1激发。用玻色子-费米子相互作用模型-2研究了几个奇a型Xe-Cs原子核，实验与计算结果吻合较好。

In this research project, nuclear quadrupole and octupole deformations have been studied from various new aspects, including both dynamical and static deformations. The theoretical tool we have used is the Interacting Boson Model (IBM). The gamma-unstable deformation is known for Xe and Ba nuclei with the mass number -130, and is described by the O (6) limit of the IBM.The O (6) limit has been considered, in a classical term, as a gamma-unstable rotor. We, however, discovered an alternative picture where all eigenstates of the O (6) limit can be constructed as multiphonon states. This new approach is called the Q-phonon scheme. The phonons are excited on the top of a deformed equilibrium in this scheme. This scheme looks quite powerful in describing states even away from the O (6) limit. For instance, yrast odd-spin states can be described as Q-phonon states except for a singular point. The quantum chaos has been further studied in terms of the rotational damping and the width. We obtained a reasonable estimate of the width, and discussed branching numbers, etc. The octupole deformation has been studied with particular attention to the electric dipole transitions. The Interacting Boson-Fermion Model-2 has been used to analyze the g factors and M1 excitaion with respect to even-even Pd isotopes and odd-A rare-earth nuclei. Several odd-A Xe-Cs nuclei have been studied in terms of the Interacting Boson-Fermion Model-2, and a good agreement between experiment and calculation has been obtained.