Computer-simulation calculations of the electronic stopping of fast heavy charges by a classical harmonic oscillator

The accuracy of Bohr’s and more recent analytical calculations of the electronic stopping of heavy charges by a classical harmonic oscillator is analyzed. According to results in this paper, for |ξ|>~100 (ξ being the Bohr stopping parameter) the present simulations agree with previous theoretical calculations, whereas for smaller |ξ| values, discrepancies are evident. In fact, for |ξ|<100 the stopping cross section seems to be sensitive to the sign of the ion charge. The so-called Barkas effect is unambiguously observed and positively charged projectiles appear to have a larger stopping compared to that of negative ones at the same ξ. Bohr’s calculations, however, seem to reproduce the stopping of negative charges relatively well, but those of positive ions are consequently underestimated. By giving the electron an initial velocity, the so-called inner-shell effect on the stopping can be readily studied. The present simulations show that previous analytical predictions of this effect do not account for the present results.