中重过渡区原子核低激发主导组态的研究

Studies of low-lying states of transitional nuclei with medium and heavy masses are one of the frontiers in nuclear structure physics. However, due to the huge dimensionality of the shell model configurations, exact shell model diagonalizations are not possible in such cases; furthermore, these nuclei are not well deformed and thus are not proper to handle by using the geometric models. Therefore microscopic and systematic calculations of low-lying states for transitional nuclei are usually difficult. The nucleon-pair approximations (NPA) of the shell model developed in last decade has been proved to be both interpretive and predictive for these nuclei. In this program we shall apply the NPA to low-lying states of medium-heavy nuclei in transitional regions. The program includes: (1) Studies of the shallow minimum of B(E2) values for even Sn isotopes at the midshell. (2) Studies of the nucleon-pair approximation with isospin symmetry and applications of this isospin dictated by pair approximation to low-lying states of unstable nuclei.

中重过渡区不稳定原子核的低激发态结构是原子核结构领域的重要前沿课题之一。然而，因为中重原子核的壳模型组态空间实在太大，不能进行严格壳模型计算，这类原子核的形变不大，也不适合几何模型处理，所以微观而系统地研究中重过渡区原子核结构理论一般比较困难。壳模型配对近似方法是这些年逐步发展起来的适合研究中重过渡区原子核低激发态的合适理论框架。本项目将采用这个理论研究中重过渡区原子核的低激发结构，主要包括：（1）研究Sn同位素链，讨论电磁跃迁性质随中子数的变化特征。（2）利用同位旋守恒的配对近似理论，研究远离稳定线的原子核结构等。

近年来随着放射性核束物理的迅速发展，不稳定原子核低激发态的研究成为原子核物理的重要前沿，其中过渡区中重质量原子核低激发态结构的理论研究日益受到人们广泛关注。本项目采用壳模型配对近似方法在中重过渡区原子核的低激发态研究中取得了系列研究成果，主要包括：（1）研究Sn同位素链的低激发磁偶极矩和B(E2)跃迁，分析波函数中不同组态的贡献，解释其电磁跃迁性质轻重质量区域不对称分布的特征。（2）研究108,109Te和109I的低激发结构（包括能级和电磁跃迁性质），分析其弱耦合图像与剩余质子中子四级-四级相互作用强度之间的关系。（3）研究自旋为3/2的“赝玻色子”的群约化规则，推导单j轨道上3个理想粒子给定总角动量I的壳模型组态的解析公式。