The recently claimed observations of non-negligible amounts of Li6 in old halo stars have renewed interest in the Big Bang nucleosynthesis (BBN) of Li6. One important ingredient in the predicted BBN abundance of Li6 is the low-energy H2(α,γ)Li6 cross section. Up to now, the only available experimental result for this cross section showed an almost constant astrophysical S factor below 400 keV, contrary to theoretical expectations. We report on a new measurement of the H2(α,γ)Li6 reaction using the breakup of Li6 at 150 A MeV. Even though we cannot separate experimentally the Coulomb contribution from the nuclear one, we find clear evidence for Coulomb-nuclear interference by analyzing the scattering angular distributions. This is in line with our theoretical description, which indicates a drop of the S24 factor at low energies as predicted also by most other models. Consequently, we find even lower upper limits for the calculated primordial Li6 abundance than before.
ASJC Scopus subject areas
- Nuclear and High Energy Physics