DOI: 10.1140/epjd/e2009-00255-9
Impact-parameter-dependent electronic stopping of swift ions
I. Binary theory
A. Schinner1 and P. Sigmund21 Institut f. Experimentalphysik, Johannes-Kepler-Universität, 4040 Linz-Auhof, Austria
2 Department of Physics and Chemistry, University of Southern Denmark, 5230 Odense M, Denmark
sigmund@ifk.sdu.dk
Received 13 May 2009 / Received in final form 13 August 2009 / Published online 3 October 2009
Abstract
A computational scheme has been developed to estimate the mean electronic energy
loss of an incident swift ion on an atomic target as a function of the
impact parameter between the moving nuclei. The theoretical basis is
binary stopping theory. In order to extract impact-parameter
dependencies it was necessary to incorporate the spatial distribution of
the target electrons. This distribution is immaterial for the stopping
cross section and straggling parameter.
Incorporating it into the existing formalism involves additional numerical
integrations. The emphasis in the present paper is laid on
verifying the reliability of the scheme. Existing theoretical estimates
with comparable input are based on the Born approximation and, more or
less explicitly, refer to incident protons. Since the present estimates are
based on classical stopping theory, a rough inverse-Bloch
correction has been developed to ensure a meaningful comparison. Good agreement is obtained
in general, and where discrepancies are found, their origin, whether in
the present scheme or the Born approximation, is discussed.
The formalism incorporates the Barkas-Andersen effect as well as
screening and shell corrections. While these effects play determining
roles in the stopping cross section, illustrating their role in the
impact-parameter dependence reveals interesting qualitative features, in
particular in the dependence on ion charge.
34.50.Bw - Energy loss and stopping power.
34.50.Fa - Electronic excitation and ionization of atoms (including beam-foil excitation and ionization).
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2009
