  The deviations from a purely exponential behavior in a decay process are
analyzed in relation to Van Hove's "\lambda^2 t" limiting procedure. Our
attention is focused on the effects that arise when the coupling constant is
small but nonvanishing. We first consider a simple model (two-level atom in
interaction with the electromagnetic field), then gradually extend our analysis
to a more general framework. We estimate all deviations from exponential
behavior at leading orders in the coupling constant.
