Direct measurement of the 2H(α,γ)6Li cross section at energies of astrophysical interest

Abstract

The knowledge of the 2H(α,γ)6Li cross section is very important to understand the production of 6Li during the Big-Bang Nucleosynthesis (BBN). Presently, no direct measurement of this reaction in the energy region of interest exists (the only direct measurements actually available are above 1 MeV in the center of mass reference frame and around the 711 keV resonance). The existing data in the energy region of interest for BBN (40 keV < Ecm < 400 keV) have been taken with indirect techniques which are affected by large uncertainties because they strongly depend on theoretical assumptions. The direct measurement is a difficult task because the expected cross section is of the order of a few pico-barn. Thanks to the natural shielding offered by the about 1400 meters of rocks, the cosmic background is reduced by a factor 106 at the Laboratori Nazionali del Gran Sasso (LNGS). Here, at the LUNA (Laboratory for Underground Nuclear Astrophysics) facility it is possible to explore with a direct measurement of the 2H(α,γ)6Li reaction cross section in the BBN energy region. This measurement can be done with a 4He intense beam hitting a windowless deuterium gas target. The emitted photons are detected with a High-Purity Germanium detector (HPGe) in close geometry. In this paper the experimental setup will be described and the measurement strategy based on the first tests already performed will be discussed.