Molecular damage induced directly and indirectly by ionizing radiation in DNA.

We describe the interaction of radiation with a double-stranded DNA molecule and with the structural water surrounding it. The results, which include a detailed picture of DNA molecular alterations, as well as their yield and spatial disposition, were obtained with the aid of Monte Carlo codes that simulate, event-by-event and simultaneously, direct and indirect effects. These calculations make use of explicit quantum-mechanical descriptions of the electronic structure of condensed water and of a homopolynucleotide chain. From these we obtain, via the dielectric response function of the two systems, epsilon (q, omega), the interaction probabilities necessary in the transport codes.