title: Absolute cross section for low-energy-electron damage to condensed macromolecules: a case study of DNA.
abstract: Cross sections (CSs) for the interaction of low-energy electrons (LEE) with condensed macromolecules are essential parameters for accurate modeling of radiation-induced molecular decomposition and chemical synthesis. Electron irradiation of dry nanometer-scale macromolecular solid films has often been employed to measure CSs and other quantitative parameters for LEE interactions. Since such films have thicknesses comparable with electron thermalization distances, energy deposition varies throughout the film. Moreover, charge accumulation occurring inside the films shields a proportion of the macromolecules from electron irradiation. Such effects complicate the quantitative comparison of the CSs obtained in films of different thicknesses and limit the applicability of such measurements. Here, we develop a simple mathematical model, termed the molecular survival model, that employs a CS for a particular damage process together with an attenuation length related to the total CS, to investigate how a measured CS might be expected to vary with experimental conditions. As a case study, we measure the absolute CS for the formation of DNA strand breaks (SBs) by electron irradiation at 10 and 100 eV of lyophilized plasmid DNA films with thicknesses between 10 and 30 nm. The measurements are shown to depend strongly on the thickness and charging condition of the nanometer-scale films. Such behaviors are in accord with the model and support its validity. Via this analysis, the CS obtained for SB damage is nearly independent of film thickness and charging effects. In principle, this model can be adapted to provide absolute CSs for electron-induced damage or reactions occurring in other molecular solids across a wider range of experimental conditions.
authors.affiliation: Groupe en Sciences des Radiations, Départment de Médecine Nucléaire et Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4. mohammad.rezaee@usherbrooke.ca
authors.forename: Mohammad
authors.initials: M
authors.lastname: Rezaee
authors.forename: Pierre
authors.initials: P
authors.lastname: Cloutier
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Bass
authors.forename: Marc
authors.initials: M
authors.lastname: Michaud
authors.forename: Darel J
authors.initials: DJ
authors.lastname: Hunting
authors.forename: Léon
authors.initials: L
authors.lastname: Sanche
mesh_terms: D004247:DNA / Q000737:chemistry* / Q000235:genetics*; D053960:DNA Breaks / Q000528:radiation effects*; D004583:Electrons; D008954:Models, Biological
chemical_list: D004247:DNA