Astrophysical reaction rates for 6He and 9Be production by electromagnetic radiative capture and four-body recombination

Abstract

The triple alpha reaction α+α+α → 12C + γ is considered to be the most relevant one in stars at the helium burning stage, since it permits to bridge the A=5 and A=8 instability gaps. However, at higher temperatures and neutron rich environments, other reactions can also play a relevant role. In this work we investigate the astrophysical reaction and production rates for the two-particle radiative capture processes α+n+n → 6He+γ and α+α+n → 9Be+γ. The hyperspherical adiabatic expansion method is used. With this method no assumption is made about the capture mechanism. The four-body recombination reactions α+α+n+n → 6He + α, α + n + n + n → 6He + n, α+α+n+n → 9Be + n and α + α + α + n → 9Be + α are also investigated as a possible alternative as a source of 6He and 9Be.