过渡区中等质量原子核结构的配对壳模型研究

With the rapid development of radioactive beam physics, studies of low-lying states of unstable nuclei with medium and heavy masses have been one of the frontiers in nuclear physics. As the configuration space of the nuclear shell model is too gigantic to handle, one has to resort to various truncations. The nucleon-pair shell model (NPSM) provides us with an appropriate framework to study the low excitations of transitional nuclei with medium and heavy masses. Therefore we propose to study the low excited states of nuclei with proton number between 20 and 50, by using the NPSM. This proposal involves of four aspects: (1) Studies of gyromagnetic factors of even-even Sn isotopes, for which we shall analyze the contribution of core excitations and explain the origin of asymmetry of electromagnetic quantities between nuclei with relatively small and large number of valence neutrons. (2) Studies of odd-mass Sn isotopes, with the focus on the evolution of the ground and low-lying states with respect to valence neutron numbers. (3) Studies of irregularities exhibited in low-lying states of Ge isotopes, and of physics mechanism of shape evolution for nuclei with neutron number N around 40 as well as collective motion of neutron-rich nuclei. (4) Studies of gyromagnetic factors for Mo, Ru, Pd and Cd isotopes, and in particular the evolution of the N=56 subshell.

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，其中过渡区中等质量的原子核低激发态结构的理论研究日益受到人们广泛关注。因为原子核壳模型的组态空间过大，所以模型空间需要截断近似，配对壳模型是很适合研究中重过渡区原子核低激发态的理论框架。本项目提出利用这一理论研究质子数在28～50之间原子核的低激发结构，主要包括：（1）研究Sn偶偶核同位素链的g因子，分析壳芯激发组态的贡献，解释其电磁跃迁性质轻重质量区域不对称分布的特征。（2）研究奇核子数的Sn同位素链，集中研究基态和低激发态自旋随中子数的演化。（3）研究Ge同位素链低激发结构随中子数的不规则变化特征、中子数N=40附近原子核形状变化的物理机制和丰中子区域原子核的集体运动。（4）研究Mo、Ru、Pd、Cd同位素链的g因子，特别是中子数N=56子壳的演化。

不稳定原子核低激发态的研究是原子核物理的重要前沿之一。本项目采用配对壳模型在过渡区中等质量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偶偶核同位素链的g因子，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）结合不同两体相互作用研究了奇核子数Sn同位素链的基态和低激发态自旋随中子数的演化；（3）研究了Ru、Cd等同位素链的电磁跃迁性质，分析了这些原子核低激发结构随中子数的变化特征；（4）研究了偶偶核108Te及其相邻奇A核的低激发主导组态，分析其弱耦合图像与剩余质子中子四极四极相互作用强度之间的关系；（5） 研究了原子核对称能的高阶项影响，特别是I^4项的模型依赖性；（6） 研究了中子i_{13/2}轨道单粒子能量上限值的鲁棒性；（7） 研究了原子核结合能的奇偶效应, 分析了不同相互作用对奇偶效应的贡献。