Reactions with 8Li at RIBRAS (Radioactive Íon Beams in Brasil): astrophysical and nuclear structure applications
A. Lepine-Szily 1*, D. R. Mendes Junior 1, P. Descouvemont 2
1 Institute of Physics, University of Sao Paulo
2 Physique Nucléaire Théorique et Physique Mathématique
Université Libre de Bruxelles, Belgium
The contribution of 8Li to the primordial nucleosynthesis [1,2,3] could modify abundances and contribute to bridge the A=8 gap, through the reaction 8Li(α,n)11B . It can explain the experimental observation of a non-negligible abundance of heavy elements in the oldest astrophysical objects . This reaction can also play an important role in the r-process nucleosynthesis and influence the seed nucleus production, necessary to the r-process to proceed [6,7].
On the other hand, the reaction 8Li(p,α)5He can be important for the depletion of 8Li and the feed back to lower masses. Thus the comparison of 8Li(p,α)5He and 8Li(α,n)11B is of genuine interest.
Measurements of the H(8Li, 4He)5He excitation function at low energies (200 keV< Ecm<2.5 MeV) were performed using the 8Li beam delivered by RIBRAS . The resonances of 9Be populated in this reaction were fitted using R-matrix calculations. This reaction populates only T=1/2 resonances and this study can shed light on spins, parities, partial widths and isospin values of high lying resonances in 9Be. A broad resonance is found at Ecm=1.7 MeV. From the total cross section the astrophysical S-factor was obtained. The increase of the S-factor near the threshold indicates the important role of sub-threshold resonances. The reaction rates of 8Li(p,α)5He and 8Li(α,n)11B in stellar environments are compared.
The interest for a simultaneous measurement of the 8Li(p,α)5He and 8Li(p,p)8Li cross sections is discussed.
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