Description
Accurate knowledge of thermonuclear reaction rates is important in understanding the generation of energy, the luminosity of neutrinos and the synthesis of elements in stars or during the Big Bang nucleosynthesis.
Due to the Coulomb barrier, the reaction cross section $\sigma(\mathrm{E})$ drops nearly exponentially with decreasing energy E. Thus, it becomes increasingly difficult to measure $\sigma(\mathrm{E})$ and deduce the astrophysical S factor S(E).
The low-energy studies of thermonuclear reactions
in a laboratory at the Earth's surface are predominantly hampered by the effects of cosmic rays in the detectors. Passive shielding around the detectors provides a reduction of gammas and neutrons from the environment, but it produces at the same time an increase of gammas and neutrons due to the cosmic-ray interactions in the shield itself. A 4$\pi$ active shielding can only partially reduce the problem of cosmic-ray background. An excellent solution is to install an accelerator facility in a laboratory deep underground. This approach
have been pursued by the LUNA collaboration (Laboratory for Underground Nuclear Astrophysics - https://luna.lngs.infn.it) installing in 1991 a 50 kV accelerator and in 2000 a 400 kV accelerator in the underground laboratories of LNGS. By the end of 2022 LNGS is planning to conclude installation and commissioning of the new 3.5 MV accelerator. In over 30 years of activity, LUNA has achieved extremely important results with major implications not only in nuclear astrophysics but also in cosmology and particle physics.