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Abstract

Observation of a threshold resonance and a new deuteron-deuteron fusion channel in accelerator experiments at extremely low energies

Konrad Czerski

Centre for Experimental Physics eLBRUS, Institute of Physics, University of Szczecin, Poland
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Direct observation of the deuteron-deuteron (DD) fusion reaction at thermal meV energies through the emission of its nuclear products, although theoretically possible, has not yet been realized. According to recent calculations, the electron screening effect, which reduces the repulsive Coulomb barrier between reacting nuclei in metal environments by several hundred eV, leads to significantly larger cross sections. They are additionally enhanced by the newly discovered threshold resonance in the compound nucleus ⁴He. This means that so-called cold fusion can be studied in the laboratory.

In this talk, I will present the results of measurements of the ²H(d,p)³H reaction performed on various deuterated metallic targets at energies below 1 keV using the ultrahigh vacuum accelerator at the University of Szczecin. The experimentally obtained yield of the ²H(d,p)³H reaction decreases by many orders of magnitude with decreasing beam energy and can be well described by the electron screening effect and the J^π = 0⁺ threshold resonance in ⁴He. In the recent experiments, the decay of this resonance by emission of an e+e- pairs has also been observed for the first time, leading to the conclusion that this new reaction channel represents the strongest channel for DD fusion at energies below 5 keV.

Furthermore, at the lowest beam energies of several keV, the reaction yield reaches a constant value, leading to the formation of a so-called plateau. As indicated by the significantly increased energies of the emitted protons, this effect can be directly linked to thermal DD fusion. The theoretical model explains the experimental results by the formation of ion tracks in the target by the projectiles, where local temperatures reach values above the melting point, leading to enhanced deuteron diffusion. The nuclear reaction rate, taking into account the enhanced screening effect and the DD threshold resonance, agrees very well with the experimental data.