ELECTRON-ENERGY-LOSS DISTRIBUTIONS IN SOLID, DRY DNA

Experimentally derived optical constants and X-ray attenuation cross s ections were used to construct the complete dipole oscillator strength distribution for solid, dry DNA. Monte Carlo simulations of the energ y loss by electrons of initial energy 5 keV to 1 MeV in DNA were perfo rmed using cumulative inelastic cross sections obtained from a formula tion incorporating the constructed dipole oscillator strength distribu tion. The energy-loss distribution, the most probable energy loss and the mean energy loss for electrons in DNA are compared to those for li quid water, gaseous water and gaseous hexane. For the most part, the c alculations show that electron energy loss in DNA is very similar to t hat in liquid water; however, it is quite different from both gaseous water and gaseous hexane. The mean energy losses for a 1 MeV incident electron in DNA, liquid water, gaseous water and gaseous hexane are 57 .9, 56.8, 50.9 and 38.4 eV, respectively. The large differences found between the predictions for DNA and for the gaseous media bring into s erious question calculations of radiation-induced damage in DNA which make use of cross sections for gaseous media. Stopping powers and cont inuous-slowing-down approximation ranges for the media for electrons a re also presented. (C) 1995 by Radiation Research Society