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

• Published in: Physical review letters Vol. 118; no. 5; p. 052701
• Main Authors: 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
• Format: Journal Article
• Language: English
• Published: United States 03.02.2017
• ISSN: 1079-7114
• DOI: 10.1103/PhysRevLett.118.052701

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.