EFFECT OF HIGH-ENERGY RESONANCES ON THE 18O(p, α)15N REACTION RATE AT AGB AND POST-AGB RELEVANT TEMPERATURES
EFFECT OF HIGH-ENERGY RESONANCES ON THE 18O(p, α)15N REACTION RATE AT AGB AND POST-AGB RELEVANT TEMPERATURES
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高能共振对 AGB 和 AGB 后相关温度下 18O(p, α)15N 反应速率的影响
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
A. Mukhamedzhanov
中科院分区：
文献类型：
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作者：
M. Cognata;C. Spitaleri;A. Mukhamedzhanov
18O(p，α)15N反应在一些天体物理场景中非常重要，因为它影响到19F、18O和15N等关键同位素的产生。通过15N的α辐射俘获，在渐近巨星壳层间区域与S元素一起合成了氟，并在18O质子诱导的破坏中产生了氟。在R型北冕恒星中观察到了特殊的18O丰度，其16O/18O≲1比银河系的值小几百倍。最后，对于AGB恒星外层形成的太阳前颗粒中的14N/15N比率没有明确的解释。同样，这样的同位素比受18O(p，α)15N反应的影响。在这项工作中，提出了一个高精度的18O(p，α)15N反应速率，基于直接测量和一个新的特洛伊木马实验的结果的同时拟合。事实上，目前的确定是不确定的，因为对19F的关键能级的共振参数知之甚少。特别是，我们重点研究了对应于19F的8.65 MeV能级的宽660keV 1/2+共振。由于Γ∼为100keV-300keV，它决定了共振对截面贡献的低能尾，并在较高能量时主导截面。在这里，我们根据我们对其共振参数的新的改进确定，提供了一个反应速率，它是T∼0.5 109K以上的两个更大的因子，这可能强烈地影响目前的天体物理模型的预测。
The 18O(p, α)15N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as 19F, 18O, and 15N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by α radiative capture on 15N, which in turn is produced in the 18O proton-induced destruction. Peculiar 18O abundances are observed in R-Coronae Borealis stars, having 16O/18O ≲ 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the 14N/15N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the 18O(p, α)15N reaction. In this work, a high accuracy 18O(p, α)15N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of 19F. In particular, we have focused on the study of the broad 660 keV 1/2+ resonance corresponding to the 8.65 MeV level of 19F. Since Γ ∼ 100–300 keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T ∼ 0.5 109 K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.