Evolution of the species produced by the slowing down of fast protons in liquid water: Simulation based on the independent reaction times approximation

We present the results of a program simulating the slowing down of fast protons in pure liquid water on short-track segments, on which the linear energy transfer (LET) remains almost constant. Spatial distributions of radical and molecular species, obtained at similar to 10(-12) s, give the starting point for the simulation of the nonhomogeneous chemical stage. The various reactions are treated in the ''independent reaction times'' approximation, which provides a good description of the partially diffusion-controlled reactions and of the coulombic interactions between the reactant pairs. The evolution of the radical and molecular yields is presented up to 10(-6) s. The results are compared for proton-track segments corresponding to different LET values ranging from 0.3 to 20 keV/mu m.