Abstract
The detection of the neutrinos produced in the p−p chain and in the CNO cycle can be used to test the Standard Solar Model. The 3He(α,γ)7Be reaction is the first reaction of the 2nd and 3rd branch of the p−p chain, therefore, the uncertainty of its cross section sensitively influences the prediction of the 7Be and 8B neutrino fluxes. Despite its importance and the large number of experimental and theoretical works devoted to this reaction, the knowledge on the reaction cross section at energies characterizing the core of the Sun (15 keV - 30 keV) is limited and further experimental efforts are needed to reach the desired (≈ 3%) accuracy. The precise knowledge on the external capture contribution to the 3He(α,γ)7Be reaction cross section is crucial for the theoretical description of the reaction mechanism. In the present work the indirect measurement of this external capture contribution using the Asymptotic Normalization Coefficient (ANC) technique is reported. To extract the ANC, the angular distributions of deuterons emitted in the 6Li(3He,d)7Be α-transfer reaction were measured with high precision at EH3e = 3.0 MeV and EH3e = 5.0 MeV. The ANCs were then extracted from comparison of DWBA calculations to the measured data and the zero energy astrophysical S-factor for 3He(α,γ)7Be reaction was found to be 0.534 ± 0.025 keVb.
Highlights
The 3He(α,γ )7Be is one of the key reactions in nuclear astrophysics, which remained critical after decades, despite the large number of experimental and theoretical studies devoted to it
In Table 1 we show the squared ANCs and their uncertainties (C
The indirectly derived ANC values can be used in future R-matrix extrapolations to increase the precision and the reliability, since they supply additional constraints on the
Summary
The 3He(α,γ )7Be is one of the key reactions in nuclear astrophysics, which remained critical after decades, despite the large number of experimental and theoretical studies devoted to it. The precise neutrino flux measurements can constrain the Standard Solar Model (SSM) and provide information on the core temperature of the Sun if the relevant nuclear reaction cross sections are known with matching accuracy. The same experimental data set was fitted using the modified two-body potential approach and significantly larger S34(0) = 0.613+−00..002663 keV b factor was found [24]. The comprehensive R-matrix extrapolation [29], including the data fitted in [2] and [24] and the recently measured higher energy cross sections [14,17,18], resulted in an S34(0) value It is clear that the calculated S34(0) factors depend strongly on the model used in the extrapolations and high precision experimental data is needed to constrain the theoretical models.
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