PARENT SESSION
9:00 AM to 11:00 AM
Sunday, April 21, 2002
Symposium 3
Clustered Radiation Damage in DNA: An Interdisciplinary Approach
Room: Nevada 8-9-10
Chair: Zimbrick, John²²Purdue University, West Lafayette, IN
Speakers: Bowman, Michael ⁴; Green, Nicholas⁵; O'Neill, Peter⁶; Wallace, Susan⁷⁴Pacific Northwest National Laboratory, Richland, WA⁵King's College, London, England⁶MRC Radiation and Genome Stability Unit, Didcot, Oxon, Ox11 ORD, UK⁷University of Vermont, Burlington, VT

(S03-2) Spatial distribution of damage events caused by low-energy electrons.

Green, Nicholas^*,1, Pimblott, Simon², ¹ Department of Chemistry, London, UK² Radiation Laboratory, Notre Dame, IN

ABSTRACT-
A specific and unique characteristic of radiation chemistry is the clustering of chemically reactive species in the radiation track. This clustering arises because of the physical properties of low-energy secondary electrons and it strongly affects the ensuing chemistry. For example in the radiolysis of water the yields of hydrogen and of hydrogen peroxide are sensitive, both to the number of reactive particles in the cluster and to their detailed spatial distribution. Similarly, in DNA the clustering of damage sites increases the complexity of damage and makes it harder to recognise and repair correctly. Cross-sections for low-energy electron interactions with water have recently been re-measured by Sanche, including energy loss to electronic excitation and ionisation, vibration and elastic scattering. These new cross-sections are employed in Monte Carlo simulations of the degradation of low energy electrons, both as a function of initial energy and averaged over a typical entrance spectrum, and validated by comparison with the EELS spectrum of ice. The numbers and types of events are investigated, with particular emphasis on the number of electronic events and the chemically reactive particles produced in them. The clustering of electronic events is analysed, and the relative spatial distributions of reactive particles produced in them is compared with the parametric models used at present. The importance of incorporating the molecular structure of the target into the simulation methodology is discussed, and two methods for doing this are proposed. Finally the chemical imperative of correctly describing the clustering and its chemical consequences is discussed.

KEYWORDS: radiation chemistry, clustered damage, low-energy electrons