Method for predicting stopping and straggling mean excitation energies

A method for the rapid and convenient evaluation of the mean excitation energies that appear in excitation-energy moments of the Bethe-Born cross section is described. It consists of an adaptation of a technique introduced by Pekeris and Dalgarno that uses the excitation-energy moments of the dipole-oscillator-strength sums. The approximate procedure proposed here requires only the initial wave function for the target. The average errors in the logarithms of the stopping and straggling mean excitation energies are less than 1% and 2%, respectively, when compared with direct calculations of these quantities for neutral atoms with nuclear charges in the 2--38 range. Certain applications require values for the subshell contributions to the stopping mean excitation energy. The present scheme provides these individual contributions with errors comparable to those observed for the total mean excitation energy