Nuclear experimental approaches towards nucleosynthesis in the universe

Abstract

All elements have been synthesized by nuclear reactions in the evolution of the universe over 13.8 billion years. Since abundances of elements rely on nuclear reaction rates among relevant atomic nuclei, nuclear physical approaches are important to clarify the nucleosynthesis in the universe. Recently, we experimentally determined the cross sections of the 7Be(n, α)4He reaction to destruct 7Be for p-wave neutrons at Ec.m. = 0.20–0.81 MeV close to the Big Bang nucleosynthesis (BBN) energy window by measuring the time-reverse reaction for the first time. This reaction was considered to be a key reaction to solve the cosmological lithium problem where the 7Li abundance predicted by the BBN theory is significantly larger than that estimated from the observations. It was suggested the calculated 7Li abundance would reduce if the destruction rate of 7Be was greatly enhanced. However, the obtained cross sections are significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the 7Be(n,α)4He reaction rate is not large enough to solve the cosmological lithium problem.