Improved information on the2H(6Li,α)4

Abstract

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.

Isospin effects on astrophysicalS-factors

“…(13) gives a value in agreement with the data. The disagreement of the obtained ratio for the reactions which include lithium isotopes again is caused by the absence of the l =0 partial wave in the entrance channel of the reaction 7 Li(p, α) 4 He. By contrast, in the case of boron involved reactions both reactions have the l =0 component [18,28] and as a matter of fact our model gives reasonable ratio for these two reactions.…”

“…By contrast, in the case of boron involved reactions both reactions have the l =0 component [18,28] and as a matter of fact our model gives reasonable ratio for these two reactions. If we use the the l = 1 term of the formula (9) for the reaction 7 Li(p, α) 4 He, we obtain 9.0, instead of 0.25, as the ratio. We can reproduce the ratio by substituting α nj by 3.3 in the former case.…”

“…Since one has factored out the strong energy dependence of σ(E) due to the barrier penetrability, the S-factor could be approximated by a smooth energy dependence in the absence of low-energy resonance. A lot of effort has been made to extract the S-factor in the low energy region in particular for transfer reactions experimentally [3,4,5,6]. Although to know the low energy S-factor for radiative capture reactions, still one needs the extrapolation with theoretical formulae [7].…”

“…Hence the screening effects of the bound electrons should be removed from the S-factor data, in order to asses the reaction rate in the stellar site correctly. The enhancement by the bound electrons is discussed in terms of a constant potential shift(screening potential U e ) [4,5,10,11,12,13]. * Also at Libera Università Kore di Enna, 94100 Enna, Italy…”

Theory of the Trojan–Horse method

“…The feasibility of the THM was studied in several experiments involving various reactions during the last years [20,21,22,23,24,25,26,27,28]. In earlier evaluations of the experiments some simplifying assumptions were made in the theoretical description.…”