Time evolution of ion states formed during the cascade decay of vacancies produced by the electron capture decay of the 125I radionuclide

Abstract

Cascade relaxation of inner-shell vacancies in tellurium atom produced by the electron capture decay of the ¹²⁵I radionuclide is studied using Monte Carlo simulations. Final cascade ions yields and mean final ion charges upon the decay of single-inner-vacancy states TeX^–15p⁵ (X = 1 s to 5 s) were calculated. The time evolution of the cascade ion states is simulated, and the mean final ion charge is found to be stabilized within τ_casc = 10^–12 s after the electron capture decay of the ¹²⁵I nucleus. This time interval must be compared to the time τ_neutr needed for ions neutralization when ¹²⁵I is used as an Auger emitter in radiotherapy. Depending on the relation between τ_casc and τ_neutr, either ‘isolated-atom’ or ‘condensed-phase’ approximation should be used in theoretical descriptions of local energy deposition.