title: Random-walk simulations of NMR dephasing effects due to uniform magnetic-field gradients in a pore.
abstract: 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.
authors.affiliation: Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands. R.M.E.Valckenborg@tue.nl
authors.forename: R M E
authors.initials: RM
authors.lastname: Valckenborg
authors.forename: H P
authors.initials: HP
authors.lastname: Huinink
authors.forename: J J v d
authors.initials: JJ
authors.lastname: Sande
authors.forename: K
authors.initials: K
authors.lastname: Kopinga