Theory of nuclear spin relaxation in disordered systems: comparison ofBloembergen–Purcell–Pound models and Monte Carlo simulations

Abstract

Two Bloembergen–Purcell–Pound (BPP) models for analysing nuclear spinrelaxation data for translational diffusion in disordered systems are comparedwith Monte Carlo simulations. One model (the a-BPP model, ‘a’ standing foraverage) is commonly used for disordered systems and the other (theCameron–Sholl BPP model) is more rigorously based and can distinguish betweensite-and barrier-energy disorder. Simulated relaxation data produced usingGaussian distributions of energy disorder are analysed using the models, and theparameters obtained from the fits are compared with the values used for thesimulations. It is found that both models can give reasonable fits to the data.Both models also give reasonable agreement with the simulation parametersprovided that the standard deviation of the energy distribution for the a-BPPmodel is interpreted as the average of the site-and barrier-energy standarddeviations. Quantitative estimates are given of the accuracy of the parametersfrom the fits.