LET dependence of cross sections for DNA strand breaks by direct effects of charged particles

In the theoretical studies described here the effects of the direct deposition of energy from the core or penumbra of a fast charged particle onto a DNA molecule in dilute aqueous solution is considered. The actual physical energy deposition processes are statistical in nature. We use stopping power formulas to calculate the average energy absorption of DNA, and Poisson statistics to obtain a detailed description of the resulting states of excitation of the molecule. The average energy of an excitation (ionization) is not known for molecules like nucleic acids or DNA, but 30 eV, a reasonable figure obtained from arguments about the absorption spectrum of water is used. Excitation of the DNA molecule is most likely followed by one of two different types of dissociation, deprotonation or direct dissociation, both of which may lead to DNA strand breaks. 2 figs