Radical yields in DNA exposed to ionizing radiation: role of energy and charge transfer

Theoretical and experimental studies of free-radical yields in oriented DNA samples exposed to ionizing radiation with high linear energy transfer at 77 K are discussed. The dependence of radical yields on the orientation of DNA chains relative to the particle flux is being investigated to gain insight into the role of intramolecular energy and charge transfer processes in radical production and decay. Model calculations based on a thermal-spike approximation are presented and their limitations for predicting the orientation dependence of radical yields observed after neutron irradiation are discussed. A more mechanistic model based on the high mobility of excess electrons in hydrated DNA is outlined. (author)