31.01.2011
Previous studies point out that the biological modifications caused in living cells by ionizing radiation are mainly due to so-called clusters of single lesions in DNA segments. The biological efficectiveness of ionizing radiation is therefore considerably influenced by the details of charged particle track structure on the scale of the DNA double-helix diameter (about 2 nm). A dominant component of track structure stems from the interaction of secondary electrons, which are responsible for a large part of radiation damage. Calculation of track structure therefore requires the cross sections of DNA constituents for electron interactions. The DNA is constructed of six molecular building blocks: four nucleic bases for encoding the genetic information, and a phosphate group and deoxyribose which form the DNA backbone.
Following the measurement of total, differential elastic and double differential inelastic electron scattering cross sections of tetrahydrofuran (which has a structure similar to deoxyribose), the differential elastic electron cross sections of trimethyl phosphate (as substitute for the phosphate group) has been determined.
The measurement was performed for electrons with kinetic energies between 20 eV and 1000 eV and for scattering angles between 5° and 135°. In addition, the elastic scattering cross sections were calculated using the modified independent-atom model [1] for energies higher than 60 eV and for scattering angles between 0° and 180°. The comparison of experimental and theoretical data shows a good agreement for electron energies of more than 100 eV. This can be seen in Figure 1 which shows the differential elastic electron-scattering cross sections of trimethyl phosphate as a function of the scattering angle for kinetic energies of 100 eV and 800 eV.
Figure : Comparison of measured (♦) and theoretical (-) differential elastic electron-scattering cross sections of trimethyl phosphate for kinetic energy T = 100 eV and T = 800 eV. The theoretical values were calculated using the modified independent-atom model [1].
Literature
A. Jain and S. S. Tayal, J. Phys. B: At. Mol. Phys. 15, L867 (1982)