Monte Carlo simulation of liquid water radiolysis by electrons and light ions

Model developed to simulate liquid water radiolysis by electrons has been applied to light ions. The model is based on Monte Carlo simulation of charged particles tracks, the Debye-Smoluchowski theory of reactions between radicals, and a random flight method to simulate diffusion of species. The model takes into account formation of ionizations, excitations and subexcitation electrons at the physical stage. Auto-ionizations and dissociations of excited molecules, hole migration, electron thermalization, geminate recombination and the case effect are considered at the physico-chemical stage. The reactions between radicals and products as well as their diffusion are simulated at the chemical stage. The decay kinetics (10-12 s - 10-5 s) of the most important radicals are reported as a function of ion energy (LET). The initial yields are independent of radiation type. At 10 μs the yields of the primary species are very dependent on track structure, especially the radical yields. Simulation suggest that for high LET particles the yields of radicals are negligible at 10μs, but not zero, they approach a limiting value. This likely reflects that the track structure is not purely cylindrical. (authors)