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Electron cross sections for the ionization of pyrimidine determined experimentally


Nanodosimetric investigations indicate that radiation-induced damage in biological systems decisively depends on the track structure of the secondary electrons in the DNA. To calculate the track structure in the nanometric range, three quantities are in general required: the doubly differential inelastic electron scattering cross section, the singly differential elastic electron scattering cross section, and the total electron scattering cross section. Pyrimidine, as a basic component of the nucleobases cytosine and thymine, is - along with deoxyribose, the phosphate group and purine - an important DNA component.

After the elastic electron cross sections had been experimentally determined, the ionization cross sections of pyrimidine were measured doubly differentially - as a function of the secondary electron energy E and of the emission angle θ for primary electron energies T between 20 eV and 1 keV. The measurement was carried out for secondary electron energies E from 4 eV up to approx. half the primary energy, and for the emission angle range from 5° to 135°. Hereby, an experimental procedure was used which allows absolute determination without the use of reference data [1].

The figure shows an example of the energy spectrum of the secondary electrons which are generated by the ionization of pyrimidine by 100 eV electrons at different emission angles.

Figure : Energy distribution of the secondary electrons generated due to the ionization of pyrimidine by 100 eV electrons at different emission angles


  1. W. Y. Baek, M. Bug, H. Rabus, E. Gargioni and B. Grosswendt, Phys. Rev. A 86, 032702 (2012)