Auger Electron Spectra - The Basic Data for Understanding the Auger Effect

Understanding the strong radiotoxicity of DNA-incorporated Auger electron-emitting nuclides requires a detailed knowledge of the nuclide's emission spectrum. A Monte Carlo computer code was previously developed to simulate Auger cascades and to provide electron spectra of 125I. To utilize experimental data for a direct validation of these simulations, the code has been adapted for cascades in xenon, which is adjacent to iodine in the table of elements. Only minor modifications of the code were necessary to obtain a very good agreement with the experimental findings. The role of shake-off electrons and the need for energy considerations during the cascades could be demonstrated. A previously published electron spectrum of 125I was recalculated and detailed results are presented here. Furthermore, to consider implications from a molecular binding of the Auger emitter, for the first time semi-empirical quantum mechanical calculations for an iodine-labelled thymine molecule were performed showing that even in the condensed phase a Coulomb explosion cannot be excluded a priori.