Emission of electrons and photons and formation of cascade ions during the decay of 125I radionuclide

Emission of electrons and photons during the cascade decay of inner-shell vacancies created after the decay of unstable 125I radionuclide is simulated by construction and analysis of the cascade decay trees in isolated-ion approximation. The yields of final cascade ions, the number of emitted electrons and photons, and their spectra, are calculated. During one transformation of 125I, the total energy emitted to the environment is 61.7 keV, of which 43.3 keV is emitted by photons, mostly high-energy KL photons produced at the first step of the decays of the 1s vacancies. If 125I is used as an agent for Auger therapy of cancer, only the energy absorbed by the tumor tissues in the nearest vicinity of the emitter is important. This energy is 18.6 keV, most of which is provided by cascade-produced electrons. The contribution of low-energy photons and cascade-produced ions to local energy deposition are 0.15 keV and 0.7 keV, respectively. Additional monopole ejection of electrons (shake off) during the cascades progression, and upon the internal conversion of 125Te* nuclide produced by the electron capture decay of 125I, is shown to affect little the final ions charges and emitted energies.