Enhanced pycnonuclear reactions in metallic environments

Study of the deuteron fusion reactions at very low energies in metallic environments enables us to determine the strength of the astrophysical electron screening effect in the terrestrial laboratories. Experiments performed under high and ultra high vacuum conditions showed that the experimentally determined screening energies corresponding to the reduction of the Coulomb barrier were significantly larger than the theoretical values calculated in terms of the dielectric function theory. As the origin of the so-called enhanced screening effect observed in nuclear reactions taking place in metals is unexplained we discuss here the interplay between a strong plasma screening and a narrow resonance placed close to the reaction threshold, which leads to the target material dependence of the reaction cross-section.