Velocity dependence of heavy-ion stopping below the maximum

Abstract

a b s t r a c tIn the slowing-down of heavy ions in materials, the standard description by Lindhard and Scharff assumes the electronic stopping cross section to be proportional to the projectile speed v up to close to a stopping maximum, which is related to the Thomas-Fermi speed v TF . It is well known that strict proportionality with v is rarely observed, but little is known about the systematics of observed deviations.In this study we try to identify factors that determine positive or negative curvature of stopping cross sections on the basis of experimental data and of binary stopping theory. We estimate the influence of shell structure of the target and of the equilibrium charge of the ion and comment the role of dynamic screening.

Expanded PASS stopping code

“…• Good agreement is generally found below the stopping maximum down to the Bohr speed [69], with the exception of He and Li ions, where our description involving a mean charge state becomes questionable.…”

“…We have repeatedly explored various options for the mean equilibrium charge on PASS output [23,69], and again in connection with the present study. Even though differences are significant, we still find that as long as all output is determined with a single jobfile, the simple Thomas-Fermi charge (10) is the best compromise.…”

Atomic limits in the search for galactic dark matter

“…3 has been clearly verified for the simplest case of antiproton stopping [17]. When one looks at a wider array of electronic stopping power data for very slow heavy ions [18], it is clear that velocity proportionality is generally observed.…”

Is electronic stopping of ions velocity-proportional in the velocity-proportional regime?

“…A few years later, direct stopping measurements in the fission-fragment range [16] suggested a linear dependence of S e on v, but with an extrapolated threshold velocity at v 2v 0 . Recent studies [17,18], however, led to the conclusion that there was no contradiction: Stopping cross sections were found to change slope mainly due to variation in equilibrium ion charge [18].…”