Modelling chemistry in radiation tracks. Some unexpected problems and possible solutions

(i) A method is described for the simulation of radical recombination in a spur, while following the simultaneous evolution of the spin function and using realistic parametrisations for the exchange interaction. We use this method to resolve an old controversy concerning the role of spin exchange in the evolution of the spur. (ii) Monte Carlo track structures are generated in a continuum, without regard for the underlying molecular configuration. Events can be generated closer to one another than the nearest neighbour distance between two water molecules. We show that this problem could have a significant effect on the modelled chemistry by superposing Monte Carlo track structures on configurations simulated by molecular dynamics.