Impact parameters for ionization by high-energy electrons

Root-mean-square impact parameters for K- and L-shell ionization by electrons with energies between 60 and 400 keV, and pertinent to energy dispersive X-ray (EDX) analysis, are calculated for a wide range of atoms. Hartree–Fock wave functions with relativistic corrections are used for the bound states and Hartree–Slater wave functions for continuum states. These impact parameters differ substantially from those given by widely used approximate formulas. Impact parameters for K- and L-shell ionization fall on a single curve, suggesting that the impact parameters are a single-valued function of the ionization threshold energy for a given incident beam energy. For the range of incident beam energies considered, impact parameters for threshold energies up to 45 keV are given in a parameterized form.