U.S. Department of Energy


Date of this Version



Published in Nuclear Tracks and Radiation Measurements 16:2-3 (1989), pp. 127-133. (Formerly International Journal of Radiation Applications and Instrumentation)


A theoretical model with no adjustable parameters is presented to evaluate the strand break yields for incident electrons between 100 eV and 1 MeV. Indirect mechanisms as well as direct mechanisms are included for the production of strand breaks. The model includes the following features: (i) multiple scattering of low energy electrons; (ii) decay of hydroxyl radicals in an aqueous solution containing Tris buffer; (iii) Monte Carlo simulation of the motion of hydroxyl radicals for interaction with the DNA sites; and (iv) stochastic aspects of the direct ionization on the DNA sites and the use of oscillator strength of a DNA molecule. The model is presented using numerical values characteristic of a dilute aqueous solution of SV40 DNA (10 μg/ml) containing 10 mM of Tris. The results have been expressed in terms of yields (indirect and direct) and D37 (indirect only) values as a function of electron energy. The yields have been normalized to breaks/rad/dalton. In the absence of experimental data with different energy electrons, the results of the present calculations have been folded into the estimation of strand breaks induced by heavy charged particles. When these results are compared with experimental data for mammalian cells under conditions such that enzymatic strand break repair is negligible, there is good qualitative agreement with the model. With the expectation that experimental data will soon be available with photons, the present model has been used to predict the strand break yields with electromagnetic radiation for thick as well as thin targets.