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Total electron scattering cross sections of pyrimidine determined experimentally

14.12.2012

The total electron scattering cross section plays a key role in electron transport calculations. As the integral sum of all interaction cross sections, it is required to determine the distance between two consecutive interaction points and is simultaneously used to check the consistency of the partial interaction cross sections used. To calculate the radiation damage in the DNA, it is therefore particularly important to know the total electron scattering cross sections of DNA components. Despite its significance, no experimental data have been available to date for the total electron scattering cross section of pyrimidine (C4H4N2), the basic component of the nucleobases cytosine and thymine in the DNA.

Given the fact that also electrons with energies below the ionization threshold can cause considerable radiation damage, the total electron scattering cross sections of pyrimidine have been measured down into the energy range below the ionization threshold.

The figure shows the energy dependence of the measured total electron scattering cross sections σt of pyrimidine for electron energies T between 5 eV and 1 keV. For comparison, the energy dependence of the values calculated with the aid of the additivity rule using the data for N2 [1] and C2H2 [2] and from the total electron scattering cross sections of benzene, which has the same number of valence electrons as pyrimidine, are depicted.

Figure : Ratio of the total electron scattering cross section σt of pyrimidine to its value at 1 keV: () present experimental results, () values calculated with the aid of the additivity rule, () benzene data by Mozejko et al., () benzene data by Sueoka.

The values determined with the aid of the additivity rule are, within the measurement uncertainty, in agreement with the experimental results over the entire energy region. The existing results are also well reproduced by the benzene data by Mozejko et al. [3], whereas they are, in the lower energy region, considerably higher than those determined by Sueoka [4].

Literature

  1. J. C. Nickel, I.Kanik, S. Trajmar und K. Imre, J. Phys. B: At. Mol. Opt. Phys. 25, 2427 (1992)
  2. O. Sueoka und S. Mori, J. Phys. B: At. Mol. Opt. Phys. 22, 963 (1989)
  3. P. Mozejko, G. Kasperski, C. Szmytkowski, G. P. Karwasz, R. S. Brusa, und A. Zecca, Chem. Phys. Letters 257, 309 (1996)
  4. O. Sueoka, J. Phys. B: At. Mol. Opt. Phys. 21, L631 (1988)