Observation of Thermal Deuteron-Deuteron Fusion in Ion Tracks

TL;DR

This study reports the direct detection of thermal deuteron-deuteron fusion in ion tracks within a ZrD2 target, demonstrating enhanced electron screening effects and a potential resonance, advancing understanding of low-energy nuclear fusion.

Contribution

It provides the first experimental evidence of thermal DD fusion at very low energies, supported by a new theoretical model involving ion tracks and phonon-induced local heating.

Findings

Electron screening energy measured at 340 eV, higher than defect-free materials.

Observation of a constant plateau yield below 2.5 keV indicating fusion.

Theoretical model aligns with experimental data, including DD resonance effects.

Abstract

A direct observation of the deuteron-deuteron (DD) fusion reaction at thermal meV energies, although theoretically possible, is not succeeded up to now. The electron screening effect that reduces the repulsive Coulomb barrier between reacting nuclei in metallic environments by several hundreds of eV and is additionally increased by crystal lattice defects in the hosting material, leads to strongly enhanced cross sections which means that this effect might be studied in laboratories. Here we present results of the 2H(d,p)3H reaction measurements performed on a ZrD2 target down to the lowest deuteron energy in the center mass system of 675 eV, using an ultra-high vacuum accelerator system, recently upgraded to achieve high beam currents at very low energies. The experimental thick target yield, decreasing over seven orders of magnitude for lowering beam energies, could be well described by the electron screening energy of 340 eV, which is much higher than the value of about 100 eV for a defect free material. At the energies below 2.5 keV, a constant plateau yield value could be observed. As indicated by significantly increased energies of emitted protons, this effect can be associated with the thermal DD fusion. A theoretical model explains the experimental observations by creation of ion tracks induced in the target by projectiles, and a high phonon density which locally increases temperature above the melting point. The nuclear reaction rate taking into account recently observed DD threshold resonance agrees very well with the experimental data.