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Description
The direct measurement of the 6Li(p, α)3He reaction at astrophysical energies using the scaled-down version of the ELISSA array has been performed at the IFIN-HH 3MV Tandetron. The 6Li(p, α)3He reaction plays a key role in stellar nucleosynthesis, being tightly bound to the well-known "Cosmological Lithium Problem" for it takes place in the context of the lithium depletion mechanisms in stars. The total cross-section for the 6Li(p, α)3He reaction has been measured before, in the proton energy range starting from 25 keV to several MeV. The so-called "Second Cosmological Lithium Problem" is concerned with the 6Li isotope primordial abundance discrepancy. It states that the measured abundance exceeds the predictions of the Standard Big Bang Nucleosynthesis theory by several orders of magnitude.
The existing 6Li(p, α)3He direct measurement data suffer from large uncertainty, particularly at energies below 500 keV (in the center-of-mass system). Thus, a new direct measurement of the 6Li(p, α)3He reaction at low energies, from 122 keV to 1.2 MeV (4 different beam energies) in the center-of-mass system has been carried out to reduce the uncertainty in the S(E) factor. In this experiment, a ∼ 2 - 4 pnA beam intensity and self-supported thin polyethylene targets (CH2, about 70 µg/cm2 thick, placed at 90º with respect to the beam axis) were used. The spot size of the 6Li beam on the target was ∼ 1 mm. The scaled-down version of the ELISSA array having 12 X3 position-sensitive strip detectors arranged in a barrel-like configuration was used to detect the transfer alpha. The solid angles of the X3 detectors have been determined from the NPTool simulation. The absolute differential cross-section of the 6Li(p, α)3He reaction has been determined by normalising to the 6Li(p, p)6Li Rutherford scattering cross-section measured in the monitor detector positioned at a 27.6º angle and located 150 mm away from the target. The total cross-sections (σtotal) of 6Li+p was obtained by fitting the angular distributions of the present data with CRC (couple reaction channel) calculations using FRESCO code. The S-factor was deduced from the total cross sections, and compared with the available compilations for 6Li(p, α)3He reaction. The present measurement resulted the S-factor with better consistency and lesser uncertainty, which will contribute to explaining the BBN network calculations.
