Ion induced radiation damage on the molecular level

Throughout our lives we are exposed to ionizing radiation from cosmic and environmental sources or from medical diagnostics and treatments. In conventional therapy of malignant tumors, photons or electrons are used. Nowadays we witness the introduction of proton and heavy ion beams which have a different distribution of the deposited dose. The dose peaks at the end of the particle's track and drops to zero beyond. In this so called Bragg peak range, where the ions have energies between zero and a few MeV, not only the deposited dose is maximum but also the relative biological effectiveness is enhanced. When ionizing radiation crosses a living cell, ionization and fragmentation of biologically relevant molecules such as water and DNA constituents occurs. These processes are the initial steps in DNA damage which in turn has the strongest biological consequences. DNA damage can have different levels of complexity leading to different biological end-points. On the molecular level ion-induced DNA damage is not yet understood. Studies on isolated gas phase molecules allow a detailed investigation of ion-induced molecular mechanisms. In this thesis, the interactions of energetic particles (He, C, H) with biologically relevant molecules (water, deoxyribose, nucleobases) and their clusters were investigated by means of high-resolution coincidence time-of-flight spectrometry. Deoxyribose molecules were found to be the most sensitive to keV ion irradiation. Energetic fragments which can induce further damage were observed in ion-induced dissociation of water molecules. In this thesis also the first step towards more realistic biological systems was taken by studying clusters. The chemical environment is indeed affecting the molecular fragmentation pathways and must be considered in future experiments.