K-shell ionization by protons: A quantitative comparison between published cross sections and theories

Abstract

The cross sections for K-shell ionization by protons available in the literature are compared to each other and to the ECPSSR theory by Brandt and Lapicki. For low scaled velocities ξ, we find that a “Coulomb correction factor” C K = exp(− λx) can explain the data, with λ increasing with target atomic number Z 2, where the variable x is proportional to ξ −3. This factor C K probably contains a residual part of the relativistic correction. For medium to high scaled velocities ξ, we average normalized experimental ionization cross sections s = σ ex σ ECPSSR over all targets, within various small intervals Δξ. The average cross sections are found to agree well with σ ECPSSR. After rejecting the data sets containing the most discrepant data, using a statistical criterion, the remaining data are almost compatible with each other. No clear evidence of a dependence of s upon Z 2 found. Empirical reference cross sections for Cu, Ag and Au targets are calculated at a few selected energies. When comparing four different SCA calculations for the ionization probability vs. impact parameter, for 2 MeV protons on Cu, we find that the curves disagree by at most 30% and that they bracket the two sets of data available.