Random-walk simulations of NMR dephasing effects due to uniform magnetic-field gradients in a pore.
A random-walk simulation program was developed to study the effect of dephasing spins in a uniform magnetic-field gradient in a porous material. It is shown that this simulation program correctly reproduces basic nuclear magnetic resonance behavior, such as the formation of a spin echo. The spin-echo decay due to dephasing in a nonrestricted medium gives the well-known exponential relation containing the cube of time, whereas the spin-echo decay due to dephasing in a porous material gives a monoexponential decay. By varying the pore size and magnetic-field gradient, the motional averaging regime and the localization regime can be simulated. Moreover, the unknown intermediate regime is investigated. By choosing the right scaling parameters, the spin-echo decay due to dephasing in a pore can be described by one master curve for all pore sizes and gradient strengths. This master curve reveals a small intermediate regime, perfectly symmetrical around the gradient for which the dephasing length is exactly equal to the structural length of the pore.
Valckenborg
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RM
Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. R.M.E.Valckenborg@tue.nl
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