中文摘要：

相互作用玻色子模型（Interacting boson model,IBM）是一个代数模型,它能很好地描述原子核的集体运动性质。由于IBM中玻色子数守恒及有可解析解,因而能方便地研究原子核过渡区的行为。本文在IBM模型中引入了一种新的方案,即用O（6）高阶项替代传统方案的SU（3）四极-四极相互作用来描述轴对称转动核。在此基础上,对过渡区具有X（5）对称性的原子核的量子相变现象进行了系统的研究。分别在两种方案下,研究了原子核^154Gd和^98Sr低激发态的能谱和电磁跃迁性质。结果表明,采用新的O（6）高阶项相互作用可以更好地描述实验结果,特别是描述不同带之间的带间跃迁性质。

英文摘要：

Background： Quantum phase transition is of great interest in many areas of physics. Purpose： In this work, a new scheme is applied to describe the transitional nuclei with X（5） symmetry, from spherical to axially deformed shape-phase transition. Methods： In this new scheme, the usual SU（3） quadrupole-quadrupole interaction is replaced by an O（6） cubic interaction in the Interacting boson model （IBM）. Results： The two X（5） candidates ^154Gd and ^98Sr nuclei are firstly investigated. The low-lying energy levels and E2 transition rates are calculated and compared with the experimental data. Conclusion： The results show that the new scheme can reasonably describe the experimental low-lying spectrum and the intraband and the interband E2 transitions. The present work is meaningful in understanding the new characteristics of symmetry by the higher order O（6） cubic interaction.