标题： 直接测量核心坍缩超新星中中微子驱动风里的弱r过程88Sr(α,n)91Zr反应的截面 显示英文标题

标题： Direct cross-section measurement of the weak r-process 88Sr(α,n)91Zr reaction in ν-driven winds of core collapse supernovae

摘要： 大约一半的铁之后的重元素已知是由快速中子捕获过程，即r-过程产生的。然而，产生r-过程的天体物理场所仍然不确定。在几个宇宙地点观测到的化学丰度表明，应有不同的机制在起作用。例如，在一些贫金属恒星中测量的银周围的丰度表明存在一个弱r-过程。这个过程可能在核心坍缩超新星的中微子驱动风中活跃，其中(${\alpha}$,n)反应主导了Z ~ 40元素在喷射物质中的合成。(${\alpha}$,n)反应的速率很少被测量，它们是从统计Hauser-Feshbach计算中确定的，使用的是${\alpha}$-光学模型势，这些仍然约束不足。因此，(${\alpha}$,n)反应速率的不确定性对从恒星建模确定的丰度的不确定性有显著贡献。在这项工作中，首次在天体物理能量下探测了影响弱r-过程丰度的$^{88}$Sr(${\alpha}$,n)$^{91}$Zr反应；在质心系中直接测量了8.37 - 13.09 MeV（3.8 - 7.5 GK）范围内的总截面。在ATLAS上进行了两次测量，使用了电分割电离室MUSIC，在反向动力学下，并遵循主动靶技术。 该反应在${\alpha}$引发的$^{88}$Sr 上的截面，位于中子数 N = 50 的壳关闭区域，被发现比预期低3倍，尽管最近的统计计算已通过邻近核素的测量得到验证。这一结果鼓励对 N = 50 和中子丰富侧的 (${\alpha}$,n) 反应进行更多的实验研究，以进一步测试此类计算的预测能力和可靠性。 显示英文摘要

摘要： About half of the heavy elements beyond iron are known to be produced by the rapid neutron capture process, known as r-process. However, the astrophysical site producing the r-process is still uncertain. Chemical abundances observed in several cosmic sites indicate that different mechanisms should be at play. For instance, the abundances around silver measured in a subset of metal-poor stars indicate the presence of a weak r-process. This process may be active in neutrino-driven winds of core collapse supernovae where (${\alpha}$,n) reactions dominate the synthesis of Z ~ 40 elements in the expelled materials. Scarcely measured, the rates of (${\alpha}$,n) reactions are determined from statistical Hauser-Feshbach calculations with ${\alpha}$-optical-model potentials, which are still poorly constrained. The uncertainties of the (${\alpha}$,n) reaction rates therefore make a significant contribution to the uncertainties of the abundances determined from stellar modeling. In this work, the $^{88}$Sr(${\alpha}$,n)$^{91}$Zr reaction which impacts the weak r-process abundances has been probed at astrophysics energy for the first time; directly measuring the total cross sections at astrophysical energies of 8.37 - 13.09 MeV in the center of mass (3.8 - 7.5 GK). Two measurements were performed at ATLAS with the electrically-segmented ionization chamber MUSIC, in inverse kinematics, while following the active target technique. The cross sections of this ${\alpha}$-induced reaction on $^{88}$Sr, located at the shell closure N = 50, have been found to be lower than expected, by a factor of 3, despite recent statistical calculations validated by measurements on neighboring nuclei. This result encourages more experimental investigations of (${\alpha}$,n) reactions, at N = 50 and towards the neutron-rich side, to further test the predictive power and reliability of such calculations.