Non-thermal processes in standard big bang nucleosynthesis: II. Two-body disintegration of D, 7Li, 7Be nuclei by fast neutrons

Continuing the analysis of non-thermal effects in standard big bang nucleosynthesis (JCAP05(2008)010), we examine the role of suprathermal nuclear reactions induced in the early universe plasma by energetic nucleons of various origins. The processes of present interest are break-ups of D, Li-7, Be-7 nuclei induced by 14-MeV neutrons generated in the plasma via the T(d,n)He-4 reaction. It is shown that this reaction forms the ensemble of fast neutrons whose fraction in the plasma neutron component is at the level of 0.01%. In spite of the small percentage, such neutrons can effectively destroy the loosely bound D, Li-7, Be-7 nuclei. It is found that at temperatures T-9 < 0.8 the n-induced non-thermal break-ups of D and Li-7 dominate over other reactions occurring in the n+D and n+Li-7 systems. However, the non-thermal neutronic effects prove to be insufficiently strong to modify the standard picture of nucleosynthesis. The D, He-3, He-4 abundances are obtained to remain unchanged, and only a little effect is marked for primordial Li-7. The 0.01% fraction of plasma neutrons (fast DT neutrons) reduces the Li-7 abundance by 0.02%.