The bare astrophysical S(E) factor of the Li-7(p, alpha)alpha reaction

The astrophysically important Li-7(p, alpha)alpha reaction has been studied via the Trojan horse method in the energy range E = 10-400 keV. A new theo retical description, based on the distorted-wave Born approximation approac h, allows one to extract information on the bare astrophysical S-factor, S- b(E), with S-b(0) = 55 +/- 3 keV barns. The results are compared with direc t experimental data leading to a model- independent value of the electron s creening potential energy, U-e = 330 +/- 40 eV, much higher than the adiaba tic limit U-ad = 175 eV.