TIME-DEPENDENT SELF-DIFFUSION BY NMR SPIN-ECHO

The relation between the NMR spin-echo attenuation in the magnetic fie ld gradient and the velocity autocorrelations of molecular random migr ation has been derived by using the comulant expansion theorem for ave raging stochastic processes. It may explain certain cases of time-depe ndent diffusion observed in many systems. In the limit of long correla tion times it is identical to Torrey's well-known formula for spin ech o attenuation due to self-diffusion. The method is used to derive the expression for spin-echo attenuation of diffusion in restricted region s.