We report on the measurement of the $^{7}$Be($n, p$)$^{7}$Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n\_TOF facility at CERN. This reaction plays a key role in the lithium yield of the Big Bang Nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and showed a large discrepancy between each other. The measurement was performed with a Si-telescope, and a high-purity sample produced by implantation of a $^{7}$Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low-energy, relative to current evaluations, in the region of BBN interest the present results are consistent with the values inferred from the time-reversal $^{7}$Li($p, n$)$^{7}$Be reaction, thus yielding only a relatively minor improvement on the so-called Cosmological Lithium Problem (CLiP). The relevance of these results on the near-threshold neutron production in the p+$^{7}$Li reaction is also discussed.

中文翻译：

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$ ^ {7} $ Be（$ n，p $）$ ^ {7} $ Li反应和宇宙锂问题：在CERN处n \ _TOF处的宽能范围内的横截面测量

我们报告了在高通量实验区（EAR2）中对从热到约325 keV中子能量的$ ^ {7} $ Be（$ n，p $）$ ^ {7} $ Li截面的测量结果位于CERN的n \ _TOF设施中。该反应在用于标准宇宙学的大爆炸核合成（BBN）的锂产率中起关键作用。此反应之前进行的仅有两次飞行时间测量，并未涵盖BBN感兴趣的能量窗口，并且显示出彼此之间的巨大差异。使用Si望远镜进行测量，并通过在CERN的ISOLDE设施中注入$ ^ {7} $ Be离子束产生高纯度样品。尽管相对于目前的评估，低能耗下的横截面明显更高，在感兴趣的BBN区域中，当前结果与从时间反转$ ^ {7} $ Li（$ p，n $）$ ^ {7} $ Be反应推断的值一致，因此仅产生了相对较小的改进关于所谓的宇宙锂问题（CLiP）。还讨论了这些结果与p + $ ^ {7} $ Li反应中近阈中子产生的相关性。