The correct prediction of the abundances of the light nuclides produced during of Big Bang Nucleosynthesis (BBN) is one of the main topics of modern cosmology. In order to precisely determine BBN 6 Li production the cross-section of the nuclear reaction 2H(α, γ)6Li must be directly measured within the astrophysical energy range of 30-400 keV. This measurement requires ultra low gamma-ray background, as obtained at LUNA, the deep underground accelerator laboratory installed in the INFN Gran Sasso National Laboratory (LNGS), Italy. On the basis of the new experimental data, the 2H(α, γ)6Li thermonuclear reaction rate has been derived. Our rate is even lower than previously reported, thus increasing the discrepancybetween predicted Big Bang 6Li abundance and the amount of primordial 6Li inferred from observations. The primordial 6Li/7Li isotopic abundance ratio has been consequently determined to be (1.5 ± 0.3) × 10^(−5) within standard BBN theory. The much higher 6Li/7Li values reported for halo stars will likely require a non-standard physics explanation, as discussed in the literature.