Threshold effect in the energy loss of hydrogen and helium ions transmitted in channeling conditions in gold single crystal

Abstract

The energy loss of hydrogen and helium ions in the low energy range (<10keV/u) in single crystal gold targets is investigated experimentally. We found that the stopping power for helium ions shows a deviation from the proportionality with ion velocity predicted theoretically. This behavior has been also observed for protons in previous experiments. Additionally, we found that for a small range of velocity the energy loss for helium ions has the same magnitude as for protons for the same velocity. This last finding is in agreement with early theoretical prediction for the ion energy loss interacting with low electron densities, beyond of metallic densities, in the frame of the free electron gas model and the density functional theory. Both effects are explained due to two particular phenomena: particle channeling in monocrystalline targets, where the inhomogeneity of the spatial electron density distribution plays a fundamental role and the well-known threshold effect in the stopping power which is explained considering the electronic band structure properties of metallic targets.