Multiple ionization and x-ray emission accompanying the cascade decay of inner-shell vacancies in Fe

Abstract

A model has been developed which predicts the relative abundances of the differently charged ions and the x-ray emission spectra resulting from the cascade decay of an arbitrary distribution of inner-shell vacancies created in atoms by energetic charged particles or x rays. The multiple-ionization and x-ray production cross sections are defined in terms of the populations of the single- and multiple-vacancy states occurring in the atomic reorganization process. All allowed radiative, Auger, and Coster-Kronig transitions are taken into account in the determination of these populations. The x-ray spectra are classified in terms of characteristic lines which are due to the radiative decay of single vacancies and satellites which are associated with transitions from multiple-vacancy states. Results of calculations are presented for the creation of the initial vacancy distribution by single inner-shell electron ionization of neutral Fe with electrons and photons. Multiple ionization is found to represent only 10% of the total for electron-impact ionization but is predicted to be predominant during $K$- and $L$-shell photoionization, in agreement with experimental results obtained for the rare gases. The intensity of the $L\alpha$ satellites is always less than the $L\alpha$ characteristic line intensity for electron-impact ionization but can substantially exceed the characteristic line intensity during $K$-shell photoionization, in agreement with previous results obtained for medium-$Z$ elements.