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Track structure simulation of electrons in pyrimidine


The extent of radiation-induced damage of the DNA can be approximated with the aid of nanodosimetric measurands. These measurands, such as the ionization cluster size, i.e. the number of ionizations of molecules generated by a primary particle within a specified volume (e.g. a short DNA section), characterize the particle track structure.

Determining nanodosimetric measurands within such small volumes is possible by simulating the track structure. These simulations require scattering cross sections for all possible interactions of the particles with DNA components (i.e. for deoxyribose, for the phosphate group, and for the four nucleobases with the basic structure of pyrimidine or purine). As secondary electrons occur in large numbers and contribute notably to radiation damage, their cross sections are of greatest significance for the simulation of the track structure.

Experimentally determined electron cross sections of pyrimidine (single differential elastic and total electron scattering cross sections) have been analyzed. From this analysis, a full set of scattering cross sections was elaborated for the simulation of the track structure (experimentally determined differential, integral elastic and total electron scattering cross sections as well as theoretically calculated total and differential inelastic cross sections).

Track structure simulations of electrons in pyrimidine show that the ionization cluster size in a volume corresponding to 10 base pairs of the DNA is similar to that of the deoxyribose-equivalent tetrahydrofuran (see Fig.). It is, however, clearly visible that for water, which is typically used as a DNA model substance in simulations, the ionization cluster size is considerably smaller at low electron energies.

Figure : Mean ionization cluster size generated by electrons in nanometric volumes of the DNA components pyrimidine and tetrahydrofuran, as well as for water.