Physico-Chemical Events

Sunday, October 16, 2005 3:00 PM-5:00 PM Exhibit Hall

(PP018) Monte Carlo simulation of water radiolysis for low-energy charged particles.

Uehara, Shuzo1, Nikjoo, Hooshang*,2, 1 School of Health Sciences, Fukuoka, Fukuoka Prefecture, Japan2 Center for Advanced Space Studies, USRA, Houston, Texas, USA

ABSTRACT- [Objectives] Among various processes in radiation-induced biological molecular effect, reactions of chemical species produced through water radiolysis are important as they could determine the yields and property of molecular damages. Chemical modules which simulate the prechemical and chemical stages of charged particle tracks in pure liquid water were developed based on physical track structure codes for electrons and low-energy protons and alpha-particles. These physical codes provide the initial spatial distribution of H2O+, H2O* and subexcitation electrons at ∼10-15 s. [Methods] Dissociation scheme in the prechemical stage (up to 10-12 s) and chemical parameters were taken from various literatures. We considered 11 chemical species and 26 chemical reactions. A step-by-step Monte Carlo approach was adopted for the chemical stage between 10-12 s and 10-6 s. The chemistry codes enabled to simulate the non-homogeneous chemistry that pertains to electron, proton and alpha-particle tracks of various linear energy transfers (LET). [Results] Time-dependent yields of chemical species produced by electrons and ions of different energies were calculated. The calculated primary yields (G values at 10-6 s) of 2.80 for OH and 2.59 for e-aq for 1 MeV electrons were in good agreement with the standard values. The LET dependence of G values at 10-6 s for a wide range of 0.2 to 235 keVm-1 was obtained. The present calculations reproduced well the published data of the LET dependence for OH and H2O2. The electron penetration ranges were calculated in order to discuss the role of low energy electrons.

Key words: Monte Carlo track structure, water radiolysis, time-dependent yields, electron penetration

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2005 RRS