Energy reemission and possible radiosensitizing effect caused by the cascade decay of single vacancies in the K, L, M, and N shells of atomic silver

Abstract

Cascade decays of single vacancies in the K, L, M, and N shells of the silver atom are studied using the method of straightforward construction and analysis of the cascade de-excitation trees with inclusion of additional shake-off ejections of outer-shell electrons caused by the change of atomic core potential due to cascade transitions. The spectra of the cascade-produced electrons and photons emitted upon the decay of single vacancies in 1s1/2 to 4p3/2 subshells are calculated. For each initial vacancy, the energies absorbed by the silver atom itself, and those carried away by cascade electrons and photons, are calculated. Absorption of energy by the silver atom itself is only significant upon N- and M-shell ionization (49–66% and 18–36%, respectively), i.e. in the UV to soft X-ray range. After L- to N-ionization, most of the acquired energy is reemitted with cascade electrons, respective portions making 81–85% during L-ionization, 62–82% during M-ionization, and 34–51% during N-ionization. Reemission of energy with cascade photons is dominant after K-ionization (76%). When silver atoms are used as radiosensitizing agents in radiotherapy, cascade electrons play the principal role in the energy transfer to organism tissues. Due to small free paths in the organic medium, they give their energy to the environment in rather small volumes inside a particular cell where they are placed. As for the photons emitted after K-ionization, they transfer energy to the medium in much larger volumes, and with much smaller absorbed doses.