Impact parameters for ionization by high-energy electrons

Root-mean-square impact parameters for K- and L-shell ionization by electro ns 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-Fo ck wave functions with relativistic corrections are used for the found stat es and Hartree-Slater wave functions for continuum states. These impact par ameters differ substantially from those given by widely used approximate fo rmulas. Impact parameters for K- and L-shell ionization fall on a single cu rve, suggesting that the impact parameters are a single-valued function of the ionization threshold energy for a given incident beam energy. For the r ange of incident beam energies considered, impact parameters for threshold energies up to 45 keV are given in a parameterized form. (C) 1999 Elsevier Science B.V. All rights reserved.