Reemission of Energy by Ionized Atoms during the Cascade Decay of Inner-Shell Vacancies

Abstract

An atom ionized in its inner electron subshell relaxes to final multiply charged ion states via the cascades of consecutive radiative and non-radiative transitions. Only a part of the energy acquired by the atom in the ionization act rests with the atom, a large amount of this energy can be reemitted into the medium by the cascade electrons and photons. The portions of energy (a) absorbed by the ionized atom itself, (b) reemitted with cascade electrons, and (c) reemitted with cascade photons are calculated for the iron, silver and gold atoms singly ionized in their inner to subvalence electron shells. Cascade decay simulations are performed using the method of construction and analysis of the cascade decay trees. The energy redistribution channel a is found to be significant only upon ionization of shallow electron subshells in the UV to soft X-ray ranges. The principal channel is b making up to 80% of the acquired energy. In Ag and Au, channel c is dominant upon K-ionization (76% and 89%, respectively). Due to small mean inelastic free paths of the cascade-produced electrons in organism tissues, they play a dominant role in localized energy transfer to the tumor cells when high-Z atoms are used as radiosensitizers in radiotherapy