108Cd能级寿命测量及其E(5)对称性研究

Investigators have shown great interested to E(5) symmetry when it was introduced. Several nuclei including 108Cd have been predicted to exhibit E(5) critical-point symmetry. However, the E(5) feature in 108Cd is still hard to be identified based on its excitation states and lacked transition probabilities of lowest-lying states. In this project, the excited states of 108Cd will be populated via inelastic neutron scattering reaction (n, n’γ), and the lifetimes of those states will be measured. The measured electromagnetic properties of those states will be reproduced by the Interacting Boson Model, then comparisons with E(5) symmetry predictions will become possible.

E(5)对称性被提出以后，就引起人们的极大关注，包括108Cd在内的数十个原子核已经被预言存在E(5)对称性。然而，仅仅根据108Cd已有的能级信息和少量的能级寿命不足以对其是否具有E(5)对称性做出严格的判断。本项目拟通过非弹中子散射反应(n, n’γ)布居108Cd的激发态，并测量相关能级的寿命，得到其电磁跃迁性质，并利用相互作用玻色子模型进行计算拟合，给出该核的E(5)对称性判据。

本项目通过熔合蒸发反应96Zr(16O, 4n)108Cd布居了108Cd的高自旋态，利用多普勒位移衰减法（DSAM）分析了其2_1^+态和4_1^+态的能级寿命，得到结果分别为6.7(7) ps和0.82(12) ps。实验结果得到的约化跃迁几率B(E2)之比B4/2为1.62(8)，与理论预言值1.56较为接近。本项目的研究结果为核结构理论模型研究原子核的集体性和E(5)对称性给出了有力的实验证据，并完善了108Cd核的能级结构信息。