Measurement of the cross section for the He-4(alpha, n)Be-7 reaction as a possible solution to the cosmological lithium problem

The cross section for the He-4(alpha,n)Be-7 reaction was measured at low energies between E-alpha = 38. 50 and 39.64 MeV motivated by the cosmological lithium problem. On the basis of the detailed balance principle, the cross section for the Be-7(n,alpha)He-4 reaction was obtained at E-c.m. = 0.20-0.81 MeV close to the Big Bang nucleosynthesis (BBN) energy window for the first time. The obtained cross sections are significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the Be-7(n,alpha)He-4 reaction rate is not large enough to solve the cosmological lithium problem.