Abstract. -In a kinematically complete measurement of the 7 Li( 7 Li,α 6 He)

The cross sections for the 6Li(n, ax) and 7Li(n, ox) reactions have been measured by the detection of a particles in coincidence with other charged particles (x). Prominent structures in the coincident a-particle energy spectra have been observed only in the case of 7Li. They could be attributed to the processes involving the states of H.The four-nucleon system is the lightest few-nucleon system to exhibit resonances at low energies. The only partide stable state is the ground state of 4He. There is now enough evidence showing that 4H and 4Li have only broad particle unstable states. Ho~ever, the data on the positions and widths of these states have often been contradictory, especially in the case of 4H.

We have studied the 2 H( 6 Li,␣) 4 He two-body reaction by applying the ''Trojan horse'' method ͑THM͒ to the 6 Li( 6 Li,␣␣) 4 He three-body reaction. The astrophysical S(E) factor has been extracted in the energy range between 10-800 keV for the two cases of target and projectile quasifree break-up. We found good agreement between the two data sets leading an improved determination of the S(E) with S(0)ϭ16.9Ϯ0.5 MeV b. Furthermore, the electron screening potential energy U e ϭ320Ϯ50 eV has been extracted in a modelindependent way by comparing direct and THM data. This value is significantly higher than the value predicted by current theoretical models.

The observational 19 F abundance in stellar environments systematically exceeds the predicted one, thus representing one of the unsolved challenges for stellar modeling. It is therefore clear that further investigation is needed in this field. In this work, we focus our attention on the measurement of the a p F , Ne 19 22

The main source of 19F in the universe has not yet been clearly identified and this issue represents one of the unanswered questions of stellar modeling. This lack of knowledge can be due to the 19F(α, p)22Ne reaction cross-section that has proven to be difficult at low energies: direct measurements stop only at about ∼660 keV, leaving roughly half of the astrophysical relevant energy region (from 200 keV to 1.1 MeV) explored only by R-matrix calculations. In this work, we applied the Trojan Horse Method to the quasi-free three-body 6Li(19F, p22Ne)d reaction performed at E beam = 6 MeV in order to indirectly study the 19F(α, p)22Ne reaction in the sub-Coulomb energy region. In this way, we obtained the cross-section and the reaction rate in the temperature region of interest for astrophysics and free from electron screening effects. A brief analysis of the impact of the new measured reaction rate in AGB star nucleosynthesis is also presented.

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