Scavenging in radiation-induced Gaussian spurs is examined with three models: (i) a Monte Carlo simulation, in which diffusion is simulated by a random walk on a cubic lattice; (ii) a master equation description based on a previously formulated independent pairs approximation for radical-radical reactions and which incorporates scavenging via a classical deterministic rate; (iii) an efficient Monte Carlo method, which is based on the first passage time distributions for the ensemble of radical-radical and radical-scavenger pairs and which assumes that these pair distances evolve independently. Model (iii) shows good agreement with the full Monte Carlo simulations, but the master equation treatment overestimates the scavenging rate because of the implicit assumption that the radicals are each centered on independent scavenger distributions. © 1985 American Chemical Society.