Computer simulation of charge recombination in model tracks of high-energy electrons in nonpolar liquids; kinetics and escape

The evolution in time of the recombination of ions in model tracks and spurs produced by high-energy electrons was calculated by computer simulation of the diffusion and drift of the ions in each other's Coulomb field. Tracks of high-energy electrons are subdivided into tracks of secondary electrons that can be considered as independent one from another. Energy losses smaller than 50 or 100 keV are assumed to give rise to correlated groups of charges. The diffusion and recombination in the groups is directly simulated. For electrons with an initial energy in excess of 50 or 100 keV calculations are performed by summing the contributions of energy losses below this value. The nonhomogeneous kinetics of the charge recombination has been studied for both the short-time and long-time domains. The survival probability as a function of time, W(t), has been calculated for the charged species in electron tracks with different initial energy of the electron, for gaussian and exponential distributions of the initial distance between the positive and the negative species. The behaviour of W(t) and comparisons with the available short-time experimental data do not provide any clear distinction between the two distributions. The behaviour of W(t) at long times was also investigated in detail. The region of applicability of the theoretical limiting behaviour t^−0.5 was checked and found to be very small. The experimentally observed behaviour t^−0.6 was critically examined. Results are obtained for the probability of ion escape from recombination in the track as a function of the initial energy of the electron. The experimentally observed decrease of the yield of escape with decreasing energy of the electron for two liquids is adequately explained.