The Trojan Horse Method Indirectly Study The Nuclear Reactions Of The Celestial Bodies From 9be At (p, Alpha) ~ 6li

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 strong test for understanding stellar structure and discriminate 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 E_G 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.However, 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)~6Lireaction, which plays a key role in beryllium burning processes, from the cross section measurement of the suitable three-body process d(9Be,a6Li)n. In this case, the deuteron is used as "Trojan Horse nucleus", having an high probability to be described as d=(p+n); in this framework the proton acts as the participant and neutron as a spectator to the virtual two-body process p+ 9Be->a+6Li. If the 9Be beam energy is higher than the Coulomb barrier, then the reaction is induced within the nuclear interaction range, thus Coulomb barrier and electron screening effect are negligible, and an indirect measurement of the bare nucleus cross section is possible. The two body bare nucleus cross section can be extracted from the measured three-body one with the relation between them given by THM theory.The d(9Be,a6Li)n experiment has been carried out at INFN-LNS in Catania, Italy. A 9Be beam provided by the 15MV SMP Tandem Van de Graaff accelerator at E=22MeV, with a spot size of about 2 mm and intensities up to 2-5 pnA, impinged on a CD2 foil target of about 190 ug/cm2. Two AE-E telescopes were used for detecting a and 6Li in coincidences. The detectors were placed at the so-called quasi-free angular pairs, where the quasi-free process contribution should be mostly present. The E signals of both telescopes were provided by position sensitive detectors (PSD).We can select a and 6Li particles with graphical cuts in the AE-E spectra. These cuts were then used for projecting data in the E1-E2 matrix. In the E1-E2 spectra, kinematical locus of the d(9Be,a6Li)n has been selected from the other possible reactions occurring in the target. The Q-value for the three-body reaction was also calculated by kinematic reconstruction. A prominent peak around Q=-0.1MeV, which is nearly equal to the theoretical value, is evident, thus giving a powerful test to the angular and energy calibration of the detectors. The kinematic locus together with Q-value and TAC spectra has been used for the three-body reaction selection. In addition, only events with spectator momentum ps<30MeV/c, for which the quasi-free reaction mechanism is dominant, were considered as recommended by THM prescription.The cross section relation between 2-body and 3-body given by THM theory wasapplied to extract the energy trend of the two body cross section. The astrophysical S(E)-factor was then extracted according to its definition after multiplying the nuclear cross section by the penetration factor. The result is plotted as a function of the center-of-mass energy Ecnl. The indirect data of S(E) extracted via the THM are normalized with direct ones. It should be noticed that the low-energy resonance (corresponding to the 6.87MeV J=l" level of 10B) is reproduced. Its width is much larger due to poor experimental energy resolution in the present experiment. An upgraded experimental setup might improve the present results and give useful information for astrophysical applications.