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

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 τcasc = 10–12 s after the electron capture decay of the 125I nucleus. This time interval must be compared to the time τneutr needed for ions neutralization when 125I is used as an Auger emitter in radiotherapy. Depending on the relation between τcasc and τneutr, either ‘isolated-atom’ or ‘condensed-phase’ approximation should be used in theoretical descriptions of local energy deposition.