Scientific news from division 6  
First more realistic simulation of the ionization cluster generation in DNA segments 

All Monte Carlo programs used previously for studying biological effects of ionizing radiation at the DNA level have calculated the track structure of the radiation in liquid water. Thus, implicitly the cross sections of water were considered as an approximation to those of the DNA. To evaluate the validity of this approximation, it is necessary to carry out numerical simulations which are based on cross sections of DNA constituents. As a first step towards this objective, the total, differential elastic and double differential inelastic cross sections for the scattering of low energy electrons on tetrahydrofuran were determined last year in Department 6.6 for a worldwide unique range of parameters. (The structure of tetrahydrofuran is very similar to the DNA constituent deoxyribose.) The dataset was parameterised by fitting theoretical models [1, 2] and integrated into the PTB Monte Carlo code for track structure simulation, which is optimized for nanodosimetry. This program was also extended to allow the simulation of a target volume whose chemical composition differs from its surrounding. The modified code was used for numerical simulations of the ionization cluster size distributions generated by electrons in a nanometric target volume corresponding in size to a short segment of the DNA double helix and surrounded by liquid water. The target volume was assumed to be filled with either liquid water or tetrahydrofuran, for which two different values of the mass density were used. One value was the density of water and the other From the calculated ionization cluster distributions, the probability of generating a
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