A stochastic cascade model for Auger-electron emitting radionuclides

TL;DR

This paper presents a Monte Carlo model for Auger-electron cascades in radionuclides, incorporating nuclear and atomic data, and validates it against literature spectra for iodine isotopes, showing good agreement.

Contribution

The paper introduces a comprehensive stochastic cascade model for Auger electrons that integrates nuclear structure, atomic transition data, and energy restrictions, advancing simulation accuracy.

Findings

Good agreement with literature data for iodine isotopes

Model accurately predicts initial vacancy distributions and energy spectra

Some discrepancies in outer-shell transition simulations

Abstract

To benchmark a Monte Carlo model of the Auger cascade that has been developed at the Australian National University (ANU) against the literature data. The model is applicable to any Auger-electron emitting radionuclide with nuclear structure data in the format of the Evaluated Nuclear Structure Data File (ENSDF). Sch\"onfeld's algorithms and the BrIcc code were incorporated to obtain initial vacancy distributions due to electron capture (EC) and internal conversion (IC), respectively. Atomic transition probabilities were adopted from the Evaluated Atomic Data Library (EADL) for elements with atomic number, Z = 1-100. Atomic transition energies were evaluated using a relativistic Dirac-Fock method. An energy-restriction protocol was implemented to eliminate energetically forbidden transitions from the simulations. Calculated initial vacancy distributions and average energy spectra of 123I, 124I and 125I were compared with the literature data. In addition, simulated kinetic energy spectra and frequency distributions of the number of emitted electrons and photons of the three iodine radionuclides are presented. Some examples of radiation spectra of individual decays are also given. Good agreement with the published data was achieved except for the outer-shell Auger and Coster-Kronig transitions. Nevertheless, the model needs to be compared with experimental data in a future study.