Rapid Communication

Abstract
Monte Carlo simulation techniques were used to calculate the probability that thymine radical anions (T ), formed by the slowing-down of high-energy protons in oriented DNA, will undergo a secondary proōtonation reaction. By assuming a large asymmetry in the thermal conductivity of oriented DNA fibres we predict a significant enhancement of protonation of T when the proton flux is incident on the sample parallel to the orientation of the DNA. These results are in qualitative agreement with experimental data on the production of TH· radicals when oriented DNA is exposed to fast neutrons.