Resonant formation of DNA strand breaks by low-energy (3 to 20 eV) electrons

Most of the energy deposited in cells by ionizing radiation is channeled in to the production of abundant free secondary electrons with ballistic energ ies between 1 and 20 electron volts. Here it is shown that reactions of suc h electrons, even at energies well below ionization thresholds, induce subs tantial yields of single- and double-strand breaks in DNA, which are caused by rapid decays of transient molecular resonances Localized on the DNA's b asic components. This finding presents a fundamental challenge to the tradi tional notion that genotoxic damage by secondary electrons can only occur a t energies above the onset of ionization, or upon solvation when they becom e a slowly reacting chemical species.