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Chair(s): Sanche, Léon
(SY046) Investigating secondary electron damage to DNA by electron stimulated desorption from thin films of DNA and its molecular components.
Bass, Andrew*,1, Sanche, Leon1, 1 Dept. of Nuclear Medicine and Radiobiology, Sherbrooke, QC, Canada
ABSTRACT- The effects of secondary electrons produced in biological cells by the passage of ionizing radiation are studied experimentally by irradiating thin (i.e., < 10 nm) bio-molecular films and related solids with energy-selected beams of low energy (i.e., < 30 eV) electrons. Electron induced effects are then monitored with a variety of surface-analytical techniques including electron energy-loss spectroscopy, low energy electron transmission spectrocopy and X-ray photon-electron spectroscopy. Of particular value have been mass spectrometric measurements of the electron stimulated desorption (ESD) of charged and neutral particles generated by fragmentation of the target film. The electron energy dependence of such yields indicate frequently the mechanisms (damage) underlying desorption and have revealed the general significance of dissociative electron attachment (DEA). Here we describe recent experiments on the ESD of fragment anionic species from double and single-stranded DNA of various preparations. The orientation of DNA strands in the target film and related properties are controlled by the inclusion of one or more thiol groups, which anchor the DNA to a gold substrate. These measurements allow the sites of electron-attack within DNA, responsible for the production of particular desorbed anions, to be identified. Results are compared with ESD measurements from films formed from smaller molecular sub-units of DNA. We will describe the development of a new-generation Time-of-flight system for ESD measurements of neutral species and illustrate its use with results from the dioxyribose analogs. A new experimental technique that uses X-ray irradiation of a supporting metallic substrate to generate a quantifiable flux of secondary electrons will be also presented. This research is supported by the CIHR.
Key words: radiation damage, low energy electrons, stimulated desorption, DNA
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