Analytical expression for K- and L-shell cross sections of neutral atoms near ionization threshold by electron impact

An analytical expression is proposed to describe the K- and L-shell ionization cross sections of neutral atoms by electron impact over a wide range of atomic numbers (4 < = Z < = 79) and over voltages U < 10. This study is based on the analysis of a calculated ionization cross section database using the distorted-wave first-order Born approximation (DWBA). The expression proposed for cross sections relative to their maximum height involves only two parameters for each atomic shell, with no dependence on the atomic number. On the other hand, it is verified that these parameters exhibit a monotonic behaviour with the atomic number for the absolute ionization cross sections, which allows us to obtain analytical expressions for the latter.