关于宇宙锂问题的\(^{7}Be(n,α)^{4}He\)反应p波截面的时间反演测量

Time-Reversal Measurement of the p-Wave Cross Sections of the ^{7}Be(n,α)^{4}He Reaction for the Cosmological Li Problem.

作者信息

Kawabata T, Fujikawa Y, Furuno T, Goto T, Hashimoto T, Ichikawa M, Itoh M, Iwasa N, Kanada-En'yo Y, Koshikawa A, Kubono S, Miyawaki E, Mizuno M, Mizutani K, Morimoto T, Murata M, Nanamura T, Nishimura S, Okamoto S, Sakaguchi Y, Sakata I, Sakaue A, Sawada R, Shikata Y, Takahashi Y, Takechi D, Takeda T, Takimoto C, Tsumura M, Watanabe K, Yoshida S

机构信息

Department of Physics, Kyoto University, Kitashirakawa-Oiwake, Sakyo, Kyoto 606-8502, Japan.

Faculty of Science, Kyoto University, Kitashirakawa-Oiwake, Sakyo, Kyoto 606-8502, Japan.

出版信息

Phys Rev Lett. 2017 Feb 3;118(5):052701. doi: 10.1103/PhysRevLett.118.052701.

DOI:10.1103/PhysRevLett.118.052701

PMID:28211732

Abstract

The cross sections of the ^{7}Be(n,α)^{4}He reaction for p-wave neutrons were experimentally determined at E_{c.m.}=0.20-0.81 MeV slightly above the big bang nucleosynthesis (BBN) energy window for the first time on the basis of the detailed balance principle by measuring the time-reverse reaction. The obtained cross sections are much larger than the cross sections for s-wave neutrons inferred from the recent measurement at the n_TOF facility in CERN, but significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the ^{7}Be(n,α)^{4}He reaction rate is not large enough to solve the cosmological lithium problem, and this conclusion agrees with the recent result from the direct measurement of the s-wave cross sections using a low-energy neutron beam and the evaluated nuclear data library ENDF/B-VII.1.

摘要

首次基于细致平衡原理，通过测量时间反演反应，在质心能量(E_{c.m.}=0.20 - 0.81) MeV下，略高于大爆炸核合成（BBN）能量窗口，实验测定了(p)波中子的(^{7}Be(n,α)^{4}He)反应截面。所得截面比从欧洲核子研究组织（CERN）的(n_TOF)设施最近测量推断出的(s)波中子截面大得多，但明显小于BBN计算中广泛使用的理论估计值。目前的结果表明，(^{7}Be(n,α)^{4}He)反应速率不足以解决宇宙锂问题，这一结论与最近使用低能中子束直接测量(s)波截面以及评估核数据库ENDF/B - VII.1的结果一致。