Abstract
Diffusion processes are studied which occur in three-dimensional media with traps at quenched random positions. For the first time, aspects of survival at intermediate times are derived, given that the concentration of traps is small. A first-order phase transition is found at zero concentration. The predictions are in good agreement with recent numerical data. They also have new implications for the Lifshitz band-edge singularity of the density of states of random binary mixtures, for a model of selfattracting polymers, and for the distribution of the number of distinct sites visited in a random walk.

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