Experimental assessment of electron ionization cross sections

Abstract

We report preliminary results of an extensive investigation of theoretical and semi-empirical calculations of electron impact ionization cross sections, detailed by individual shells: they encompass the well known tabulations of the EEDL data library (also distributed within ENDF/B-VII) used by Geant4, MCNP and other codes, recent calculations used in Penelope, as well as other models not yet used in general-purpose Monte Carlo transport codes. All models have been subject to a rigorous validation test against a wide collection of experimental measurements. Special attention has been devoted to possible sources of systematics affecting the validation process, both of physical and mathematical origin. As most of the data reported in the literature as experimental measurements of ionization cross sections actually derive from X-ray production measurements, the systematic effect of different compilations of fluorescence yields has been quantitatively assessed. The compatibility of calculated and experimental cross sections has been further examined with categorical analysis methods to determine whether the observed differences across the various models are statistically significant. The results of this validation process identify objectively and quantitatively the state of the art in modeling electron impact ionization; they are relevant for the improvement of ionization modeling in Monte Carlo codes.