摘要:
慢速中子俘获过程(s 过程) 是合成比铁重元素的重要途径之一.22Ne(α, n)25Mg反应是大质量AGB星中s 过程主要的中子源,其中的22Ne 主要通过14N(α, γ)18F(β+)18O(α, γ)22Ne 反应链合成.该反应链中关键反应18O(α, γ)22Ne在天体物理感兴趣能区的截面非常低,其天体反应率主要来自于22Ne α分离阈附近低能共振态的贡献,但目前相关能级的共振参数严重缺失.在HI-13 串列加速器的Q3D 磁谱仪上,通过测量18O(6Li, d)22Ne 反应的角分布,利用DWBA分析确定了22Ne 分离阈附近共振能级Eα = 470 keV 的自旋宇称为0+,为后续计算18O(α, γ)22Ne 的天体反应率打下了基础.
Abstract:
About a half of the abundances of elements heavier than iron comes from the so-called slowneutron capture process (s-process) in Asymptotic Giant Branch (AGB) stars,with the 22Ne(α, n)25Mg reaction as one of the main neutron sources. In the beginning phase of AGB thermal pulse, 22Ne is produced by the 14N(α, γ)18F(β+)18O(α, γ)22Ne reaction sequence, in which the 18O(α, γ)22Ne reaction plays a key role. While the reaction rate of the 18O(α, γ)22Ne is mainly affected by several resonant states lying closely to the α threshold in 22Ne, up to now, the relevant 22Ne parameters are fragmentary in the energy region corresponding to the typical temperatures of s- process. The direct measurement of the 18O(α, γ)22Ne reaction rate is extremely difficult due to the very low cross section. In this work, we investigated the 22Ne resonant states via the 18O(6Li, d)22Ne reaction at the Beijing HI-13 tandem accelerator of China Institute of Atomic Energy. Based on the DWBA analysis, preliminary results showed that the spin-parity of 22Ne Eα=470 keV resonant states was assigned as 0+, which would make contributions to subsequent calculation for the reaction rate of the 18O(α, γ)22Ne.
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