Study Of The Reaction ～9Be(p,α)～6Li Via The Trojan Horse Method

In order to understand many astrophysical processes a complete knowledge of microphysics is required. Nuclear Astrophysics plays a key role in the description of astrophysical phenomena: it studies the nuclear processes that have been taking place in the universe since its beginning.Beryllium primordial abundances can provide a powerful test to discriminate between homogeneous and inhomogeneous primordial nucleosynthesis. Moreover, the study of beryllium abundances in young stars, together with lithium and boron, can provide a strict test for understanding the stellar structure and discriminating between possible non-standard mixing processes in stellar interiors.In both stellar and primordial environments, however, Li,Be and B are mainly destroyed by proton-capture reactions via the (p,α) channel with a Gammow energy EG ranging from ~10keV (for stellar nucleosynthesis) to ~100 keV (for primordial nucleosynthesis). These energies are much lower than the Coulomb barrier EC, which is usually of the order of MeV's. Thus the reactions take place via tunnel effect with an exponential decrease of the cross section. Due to the exponential suppression, the behavior of the cross sections at astrophysical energies are usually extrapolated from that at higher energies by using the definition of the astrophysical factor S(E), which varies smoothly with energies. Nevertheless this extrapolation procedure can introduce some uncertainties due to the presence of unexpected sub-threshold resonances or electron-screening effects.In recent years, many indirect methods have been developed in order to extract the S(E)-factor without extrapolations. In particular, the Trojan-Horse Method (THM) is a powerful tool, which selects, under appropriate kinematical conditions, the quasi-free (QF) contribution of a suitable three-body reaction performed at energies well above the Coulomb barrier to extract a charged particle two-body cross section at astrophysical energies, free of Coulomb suppression and electron-screening effect.The THM is applied to derive the bare nucleus cross section of the ~9Be(p,α)~6Li reaction, which plays a key role in beryllium burning processes, from the cross section measurement of the suitable three-body process d(~9Be,α~6Li)n. In this case, the deuteron is used as"Trojan Horse...