Dynamical Electron Screening in Radioactive Decays

Abstract

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

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“…Here α is the fine-structure constant, Z 1 and Z 2 are the charges of reacting particles and µ is the reduced mass. The screening energy values, obtained earlier under HV conditions, reported in [2] and that obtained under UHV conditions [8] together with the theoretical calculations are presented in Table I. Those, astonishingly large discrepancies provide grounds to expect a resonance contribution to the reaction cross-section.…”

“…[10] a 0 + single-particle resonance in 4 He assumed at E R = 10 eV with the width of 10 eV could explain the experimental cross-section enhancement at low energies with a theoretical screening energy U e in Zirconium as presented in Fig. 2.…”

“…Since contamination of the target surface plays a crucial role in the screening experiments we performed a series of new experiments dealing with atomically clean targets under ultra-high vacuum (UHV) conditions [7,8]. The resulting screening energies turned to be remarkably larger than the previous experimental values, stepping up the discrepancy to the theoretical data.…”

New Experimental Constraints on the Electron Screening Effect in Astrophysical Plasma

“…The difference between the theoretical and experimental data is clearly visible. New measurements, obtained under UHV conditions yielded U e = 497 ± 3 eV, thus increasing the difference between theoretical and experimental data [8].…”

“…However, the comparison between experimental and theoretical data is difficult because of some systematic errors in experiments, resulting especially from oxidation of the target surface during the measurements. A series of new experiments dealing with atomically clean targets under ultra-high vacuum (UHV) conditions [7,8] result in screening energies larger than the previous experimental values, escalating the discrepancy to the theoretical expectations. Thus, we discuss here an alternative source of the experimentally measured enhanced screening effect resulting from a narrow resonance close to the reaction threshold.…”