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Abstract

The influence of molecular diffusion on nmr spin echo signals using pulsed field gradients is investigated theoretically in the case of heterogeneous systems in which the motion of the molecules can be described by two different diffusion coefficients.

The method is similar to that used by Beckert and Pfeifer for calculating correlation functions in two phase systems.

It is shown that in general the above mentioned diffusion process leads to a superposition of two exponential curves. Some special cases are discussed.