Direct measurement of the ⁷Be(n, α)⁴ He reaction cross sections for the cosmological Li problem

Abstract

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 close to 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.