RESUMEN
PURPOSE: One important obstacle in modeling the biological damage of 125I lies in the collective effects of the emitted electrons. The huge number of possible different ways of atomic rearrangement causes a strong variability in the number and energies of the emitted electrons. The aim of this work is to tabulate, separately for each atomic rearrangement pathway, the absorbed doses and the single-strand breaks (SSB) probabilities for different size nanospheres of liquid water. METHODS: A simple deterministic (non-stochastic) atomic rearrangement model of only 265 pathways is appropriate for modeling the electron-capture and internal conversion processes in 125I. The feasibility of the atomic rearrangement model is verified by comparing the SSB yield for ultrasoft X-ray sources with Lobachevsky's experimental data. RESULTS: A linear equation is sufficient for describing the SSB probability as a function of the dose absorbed in a small volume surrounding the labelled nucleotide 125I-dC. CONCLUSIONS: The application of a deterministic atomic rearrangement model to Auger electron emission spectra gives a new perspective to the study of low linear energy transfer (LET) radiation effects on DNA. The damages induced by point electron-capture (EC) sources and by macroscopic X-ray sources are compared.
Asunto(s)
Daño del ADN , ADN/efectos de la radiación , Electrones , Radioisótopos de Yodo , ProbabilidadRESUMEN
The standardization of radionuclides decaying by electron capture can be carried out in LS counters by the CIEMAT/NIST method. The KLM model considers a simplified atomic rearrangement model in which all L- and M-subshells have been averaged. In this paper, instead of considering the 22 rearrangement pathways of the KLM model, we concentrate our analysis on the pathways corresponding to L-Auger electron transition. It is proved that the counting efficiency depends strongly on the energy E(LMM). Therefore, it is important to know the optimum value for E(LMM) and how to obtain it. To this end, the equations of the probabilities and the reduced energies for 3816 atomic rearrangement pathways have been derived. To average the equations, a computer program called MOYEN has been developed. The energy E(LMM) has been computed for 55Fe and 125I from different mean value definitions.
Asunto(s)
Algoritmos , Electrones , Modelos Químicos , Radioisótopos/análisis , Conteo por Cintilación/métodos , Programas Informáticos , Simulación por Computador , Dosis de Radiación , Radioisótopos/químicaRESUMEN
Ionization quench function Q(E) introduces an important correction in the CIEMAT/NIST tracing method. In this paper we present a detailed analysis of the equations used to compute the counting efficiency of 55Fe. The counting efficiency of this radionuclide is very sensitive to the shape and values of Q(E) for this method. We demonstrate that the Birks equation and stopping power are not adequate to obtain low discrepancies between the experimental and computed efficiencies. An empirical procedure to compute accurate Q(E) functions is also given.