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。~(22)Ne(α, n)~(25)Mg反应是大质量AGB星中s过程主要的中子源,其中的~(22)Ne主要通过14N(α,γ)18F(β+)18O(α,γ)~(22)Ne反应链合成。该反应链中关键反应18O(α,γ)~(22)Ne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~(22)Neα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)~(22)Ne反应的角分布,利用DWBA分析确定了~(22)Ne分离阈附近共振能级Eα=470 ke V的自旋宇称为0+,为后续计算18O(α,γ)~(22)Ne的天体反应率打下了基础。
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~(22)Ne(α, n)25 Mg reaction as one of the main neutron sources. In the beginning phase of AGB thermal pulse,~(22)Ne is produced by the14 N(α, γ)18 F(β+)18 O(α, γ)~(22)Ne reaction sequence, in which the18 O(α, γ)~(22)Ne reaction plays a key role. While the reaction rate of the18 O(α, γ)~(22)Ne is mainly affected by several resonant states lying closely to the α threshold in~(22)Ne, up to now, the relevant~(22)Ne parameters are fragmentary in the energy region corresponding to the typical temperatures of s-process. The direct measurement of the18 O(α, γ)~(22)Ne reaction rate is extremely difficult due to the very low cross section. In this work, we investigated the~(22)Ne resonant states via the18 O(6 Li, d)~(22)Ne 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~(22)Ne Eα=470 ke V resonant states was assigned as 0+, which would make contributions to subsequent calculation for the reaction rate of the18 O(α, γ)~(22)Ne.
引文
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