Recombination and escape of ions in high-energy charged particle tracks: Computer simulation compared with the analytical model of Jaffe

Computer simulations have been carried out of the movement due to diffusion and drift in each other's field of ions in cylindrical tracks, representative for tracks of protons in the megaelectronvolt region in nonpolar molecular liquids. The recombination and the escape of the ions from the track, in the absence and presence of external electric fields, has been calculated. The decay in time of the number of ions due to recombination in the tracks is remarkably well described by the analytical treatment of Jaffe in 1913, when the Debye-Smoluchowski rate coefficient is used. It is concluded that the Debye-Smoluchowski expression, derived for dilute solutions (single pair interactions), is also valid for large concentrations. For low and moderate fields the ion escape yields as obtained by the Jaffe treatment are unsatisfactory. In this case the field effect is observed to resemble the behavior as given by the expression of Onsager for single pairs, in agreement with earlier theoretical predictions. For very large fields the ion escape yields obtained with the Jaffe treatment are in fair agreement with those of the simulations.