The reaction cross-section has been measured for deuteron energies below 25 keV in a deuterized Zr target under improved ultra-high-vacuum conditions and controlled target surface contamination. The increase of reaction enhancement factors towards lower energies is much weaker than that determined before and can result not only from the electron screening effect but also from a suggested 0+ threshold resonance in 4He. The cross-section calculations performed within the T-matrix approximation enable to estimate a coherent resonance contribution and explain the observed energy dependence of the enhancement factors. Additionally, indications for the increase of the screening energies due to impurities at the target surface could be found.

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Recently, the electron screening effect in metallic environments has been experimentally investigated by many groups in low-energy nuclear reactions. The similar effect is expected in radioactive decays where the decay constant should be dependent on the valence electron density of the host material. Since metals represents a very good model for dense astrophysical plasmas, comparison of both effects can deliver new information about mechanism of the enhanced electron screening and consequences for nuclear processes taking place in stellar interior. Here, we present a new experimental investigation of screening effect in the d + d nuclear reactions under UHV conditions. Based on those experimental results a host material dependence of the alpha decay probability has been predicted. 10th Symposium on Nuclei in the Cosmos

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.