Astrophysical S-factor of T(4He, γ)7Li reaction at E cm = 15.7 keV

The astrophysical S-factor of the reaction T(⁴He, γ)⁷Li is measured for the first time at the center of mass energy E_cm = 15.7 keV, lower than the energy range of the Standard Big Bang Nucleosynthesis (SBBN) model. The experiment is performed on a Hall pulsed accelerator (TPU, Tomsk). An acceleration pulse length of 10 μs allows one to suppress the background of cosmic radiation and the ambient medium by five orders of magnitude. A beam intensity of ~ 5 × 10¹⁴⁴He⁺ ions per pulse allows one to measure an extremely low reaction yield. The yield of γ-quanta with the energies E_γ⁰= 2483.7 keV and E_γ¹= 2006.1 keV is registered by NaI(Tl) detectors with the efficiency ɛ = 0.331 ± 0.026. A method for direct measurement of the background from the chain of reactions T(⁴He, ⁴He)T→T(T, 2n)X→(n, γ) and/or (n, n'γ) which ends by neutron activation of materials surrounding the target is proposed and implemented in this study. The value of the astrophysical S-factor of the reaction T(⁴He, γ)⁷Li S_αt(E_cm = 15.7 keV) = 0.091 ± 0.032 keV b provides the choice from the set of experimental data for the astrophysical S_αt-factor in favor of experimental data [4] with S_αt(E_cm = 0) = 0.1067 ± 0.0064 keV b.