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Ionization Cross Sections and Dissociation Channels of DNA Bases by Electron CollisionsFree secondary electrons are the most abundant secondary species in ionizing radiation. Their role in DNA damage, both direct and indirect, is an active area of research. While indirect damage by free radicals, particularly by the hydroxyl radical generated by electron collision with water. is relatively well studied, damage by direct electron collision with DNA is less well understood. Only recently Boudaiffa et al. demonstrated that electrons at energies well below ionization thresholds can induce substantial yields of single- and double-strand breaks in DNA by a resonant, dissociative attachment process. This study attracted renewed interest in electron collisions with DNA, especially in the low energy region. At higher energies ionization becomes important. While Monte Carlo track simulations of radiation damage always include ionization, the probability of dissociative ionization, i.e., simultaneous ionization and dissociation, is ignored. Just like dissociative attachment, dissociative ionization may be an important contributor to double-strand breaks since the radicals and ions produced by dissociative ionization, located in the vicinity of the DNA coil, can readily interact with other parts of the DNA. Using the improved binary-encounter dipole (iBED) formulation, we calculated the ionization cross sections of the four DNA bases, adenine, cytosine, guanine, and thymine, by electrons at energies from threshold to 1 KeV. The present calculation gives cross sections approximately 20% lower than the results by Bemhardt and Paretzke using the Deutsch-Mark and Binary-Encounter-Bethe (BEB) formalisms. The difference is most likely due to the lack of a shielding term in the dipole potential used in the Deutsch-Mark and BEB formalisms. The dissociation channels of ionization for the bases are currently being studied.
Document ID
20040084406
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Huo, Winifred M.
(NASA Ames Research Center Moffett Field, CA, United States)
Dateo, Christopher E.
(Eloret Corp. Moffett Field, CA, United States)
Fletcher, Graham D.
(Eloret Corp. Moffett Field, CA, United States)
Date Acquired
August 21, 2013
Publication Date
March 12, 2004
Subject Category
Life Sciences (General)
Meeting Information
Meeting: 8th International Workshop Radiation Damage of DNA
Location: Banff
Country: Canada
Start Date: May 25, 2004
End Date: May 30, 2004
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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