The ² H(d,p) ³ H reaction in metallic media at very low energies

Abstract

Abstract. -Based on our experimental studies of the electron screening effect in the 2 H(d, p) 3 H reaction for five deuteron-implanted solid targets (C, Al, Zr, Pd, Ta), theoretical calculations have been performed within an improved dielectric function theory. The theory describes correctly the observed target material dependence of the screening energies, underestimating, however, the absolute values by about a factor of 2. Applying an effective screening energy approach, the theoretical cross-sections, thick-target yields as well as nuclear reaction rates have been calculated down to the energies corresponding to the conditions of so-called cold-fusion experiments. This allows for a comparison of the experimental results at higher energies with those achieved in the heavy-water electrolysis experiments.Introduction. -Nuclear reaction rates at very low projectile energies, far below the Coulomb barrier, are sensitive to the electronic properties of target materials. The electrons surrounding the reacting nuclei can increase the tunneling probability through the Coulomb barrier leading to an enhancement of nuclear reaction rates at low projectile energies. The electron screening effect was originally discussed due to its importance for dense astrophysical plasmas, where nuclear reaction rates can be increased by many orders of magnitudes [1]. Experimentally, the screening effect could be verified only fifteen years ago in gas target experiments [2] by an observation of an exponential-like increase of the measured cross-section for decreasing projectile energies compared to the cross-section expected for bare nuclei. Theoretically, this effect was described [3] by applying a conception of the electron screening energy resulting from the gain in the electron binding energy between the initially separated atoms and the finally united atom. In the experiments, the screening energy could be treated as an energy shift of the kinetic energy of the reacting nuclei causing an increase of the penetration probability through the Coulomb barrier.

Accelerator Experiments and Theoretical Models for the Electron Screening Effect in Metallic Environments

“…So any conclusion based on the observed material dependence of the screening energies is premature. On the other hand, the theoretical calculations performed within an improved dielectric function theory [11,15] predict only a weak material dependence of U e in contradiction to the experimental results of [7,8,9]. Furthermore, an error of 100 eV implies an error in the reaction rate of many orders of magnitude when extrapolating to room temperature, i.e.…”

“…In [11,15] we presented a analytical model based on the dielectric function theory for the description of the screening effect and extrapolation to room temperatures. It remains, however, below the measured screening energies by a factor of 2 though better than other approaches cited therein.…”

Dynamical Electron Screening in Radioactive Decays

“…In addition, the discrepancies between the theoretical predictions and the experimental results have been found [8]. The absolute values of experimental screening energies are by a factor of two smaller than those calculated in the framework of the self-consistent dielectric function theory.…”

Evidence for a host-material dependence of the n/p branching ratio of low-energy d+d reactions within metallic environments

“…The dense bound and free electrons in the metal can abate the Coulomb barrier in a dynamic process prior to the reaction generating a gross enhancement of the cross section which can still not be described by theory to this extent [19]. Both are dynamic processes.…”

“…Thus making it, together with the enhanced electron screening in metals [19], more credible although further efforts are necessary. An experiment with more sophisticated particle detection techniques is in progress in order to refine the data.…”