COMPUTER-AIDED STOCHASTIC MODELING OF THE RADIOLYSIS OF LIQUID WATER

A computer-aided stochastic model of the radiolysis of liquid water ha s been developed. It is based on Monte Carlo simulation of charged-par ticle tracks, a random-flight method to simulate diffusion of species and the Debye-Smoluchowski theory of reactions between radicals. The m odel takes into account the formation of ionizations, excitations and subexcitation electrons at the physical stage. The corresponding initi al yields at similar to 1 fs were found to be G(ion) = 4.37, G(exc) = 2.81 and G(e-sub) = 4.38. The energy spectrum of subexcitation electro ns has been calculated. Autoionizations and dissociations of excited m olecules, hole migration, electron thermalization, geminate recombinat ion and the cage effect are considered at the physico-chemical stage. The mean thermalization distance of subexcitation electrons is 24.5 nm . The initial yields of e(aq)(-), H+, OH, H, H-2 and O are 4.89, 4.86, 5.96, 1.10, 0.15 and 0.15, respectively. The reactions between radica ls and products as well as their diffusion are simulated at the chemic al stage. The decay kinetics of the most important radicals is reporte d together with the time evolution of the most important reactions. Th e yields of the reactive radicals, e(aq)(-), H+, OH, H and OH-, at 1 p s are 4.84, 4.85, 5.87, 1.09 and 0.0, respectively. The respective ste ady-state yields at 10 mu s are 2.70, 3.58, 2.89, 1.17 and 0.79. The y ields of molecular products, H2O2 and H-2, are 0.73 and 0.47 at 10 mu s. The concentration-dependent yields of e(aq)(-), OH and H2O2 are cal culated in three different aqueous solutions. The predictions of the m odel agree fairly well with experimental data. (C) 1998 by Radiation R esearch Society.