Spin-echo decay in a stochastic field environment

We derive a general formalism with which it is possible to obtain the time (tau) dependence of the echo size for a spin in a stochastic field environment. Our model is based on "strong collisions." We examine in detail two examples. Tn the first one the field distribution has a finite second moment, and in the second one (a Lorentzian) it does not. We find that the echo decay in the first case is exponential in tau(3) as tau-->0, and in the second case can be approximated by the phenomenological expression exp(-[2 tau/T-2](beta)) with 1<beta<2; in the tau-->0 limit beta=2. In addition, only the first case shows a T-2 minimum effect. [S0163-1829 (99)02937-9].