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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.

Abstract. -The 12 B excitation energy spectrum has been obtained from coincidence measurements of the 9 Be+ 7 Li −→ 2α+ 8 Li reaction at E0=52 MeV. The decay of the states at excitations between 10 and 16 Mev into α+ 8 Li has been observed for the first time. Observed α-decay indicates possible cluster structure of the 12 B excited states. The influence of these states on the cross section of the astrophysically important 8 Li(α,n) 11 B and 9 Be+t reactions is discussed and the results are compared with existing results.Introduction. -Light nuclei are interesting in their own right as almost every nucleus possesses some unique properties which are fingerprints of its quantum structure. Their extremely varied structures, from spherical shell model shapes to prominent clustering, are a considerable challange to understand and model. Although light nuclei have been studied intensively for many decades, very limited and often contradictory information exist for many of them. That is also the case for 12 B nucleus. It is interesting to draw a comparison with its structure and structures of the 11 Be, 11 B, 12 Be and 12 C nuclei which all show prominent α-clustering. As an example, 11 B and 12 C nuclei are typical cluster nuclei and their α-decays were experimentally observed in many particle coincidence measurements some 40 years ago (e.g. [1, 2], for full list of the references see [3]). The helium decays of 12 Be nucleus were reported only recently [4], but there is no experimental results on the α-decays of 12 B. Some experimental indications for cluster structure of 12 B states come from the measurements of the 8 Li(α,n) 11 B reaction. According to inhomogenous models of big bang nucleosynthesis this reaction would have had a crucial role in the production of A ≥ 12 nuclides [5, and references therein]. Hence this reaction and the states of 12 B at excitations close to the α-8 Li separation energy (E s =10.001 MeV) have attracted special interest. The 1996 status of the results obtained from both direct and indirect measurements was critically reviewed in [6]. Results from a recent direct measurement of the reaction [7] disagree with the conclusions from [6]. The reaction cross section obtained in that exclusive measurement at c.m. energies between 1.5 and 7 MeV is almost a factor of 2 lower than that obtained in previous inclusive measurements.

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