High-energy breakup of 6Li as a tool to study the Big Bang nucleosynthesis reaction 2H(α,γ)6Li

Physical Review C (Impact Factor: 3.72). 11/2010; DOI: 10.1103/PhysRevC.82.065803
Source: arXiv

ABSTRACT The recently claimed observations of non-negligible amounts of 6Li in old halo stars have renewed interest in the Big Bang nucleosynthesis (BBN) of 6Li. One important ingredient in the predicted BBN abundance of 6Li is the low-energy 2H(α,γ)6Li 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 2H(α,γ)6Li reaction using the breakup of 6Li 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 6Li abundance than before.

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    ABSTRACT: A new cosmological model of LiBeB production in the first structures has been performed. This was motivated by observations of 6Li in halo Pop II stars that indicated a potentially high abundance of this isotope, about a thousand times higher than its predicted primordial value. Using a cosmological model for the cosmic ray-induced production of this isotope in the IGM allows us to explain the observed abundance at very low metallicity. Given this constraint on the 6Li, we also calculate the non-thermal evolution with redshift of D, Be, and B in the IGM, and the resulting extragalactic gamma-ray background. The computation is performed in the framework of hierarchical structure formation considering several star formation histories including specifically Pop III stars. We find that spallative D production is negligible and that a potentially detectable Be and B plateau is produced by these processes at the time of the formation of the Galaxy (z˜3).
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