https://doi.org/10.1351/goldbook.09370
Simplification of calculations involving the energy of an ion passing through a solid sample, where the energy of the ion at the surface is used in place of a properly averaged energy.
Note: This approximation is used to determine the energy at which scattering cross sections (see elastic scattering cross section, inelastic scattering cross section) or stopping cross sections, or both, are evaluated.