Year

2014

Degree Name

Doctor of Philosophy

Department

School of Physics

Abstract

This work provides the first set of electron-impact interaction cross section data of DNA constituents based on experiments. These data permit to investigate the accuracy by which water cross sections can be used to represent DNA media in track structure simulations of electrons with energies between 7 eV and 1 keV. Liquid water or water vapour is conventionally used in track structure simulation codes to estimate radiobiological effects, however, the interaction cross sections of liquid water have not been experimentally verified.

Initially, electron track structure simulations in liquid water with the codes PTra and Geant4 were benchmarked with respective experimental literature data. For this purpose, PTra was augmented with reviewed water cross section data for electrons and protons. The evaluated cross section data for electron impact on the DNA constituents tetrahydrofuran, trimethylphosphate, pyrimidine and purine were implemented in PTra for simulations of monoenergetic electrons in DNA media. The DNA media consisted of a composition of DNA constituents with different water content. Due to substantial differences in the cross section data of water and DNA constituents, a significant enhancement of calculated clustered ionisation and excitation events in DNA media relative to water was observed for electrons with energies below 150 eV. In consequence, the probability to produce biologically relevant ionisation clusters in the vicinity of a 1 MeV proton track is higher for DNA media compared to water.

As a first step towards modelling the transport of ions in DNA medium, simulations of protons (0.1–10 MeV) and alpha particles (0.1–20 MeV) in nitrogen and propane were benchmarked by comparing simulated and measured nanodosimetric quantities.

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