Nuclear Magnetic Relaxation of Nonuniform Systems

Abstract

The relationship between the relaxation time measured for a heterogeneous system and the relaxation times and concentrations of the components is discussed. In general, the value of the ``average'' relaxation time observed is dependent upon the method of measurement. When the relaxation effects are completely averaged out within the time of measurement, the system behaves as a single phase while the relaxation time is determined by the time average (or mass average) of 1/T. If no averaging takes place at all the signal strength is determined by the sum of the magnetizations of the components, each with its own relaxation time. In the transition case one should use the concept ``amount of relaxation during time t'', ∫₀^t dt′/T. Two examples of this transition have been examined experimentally. They are determined by the phenomena of diffusion and adsorption, both of which are able to delay the completion of the ``relaxation life cycle.'' The protons in hydrocarbons mixed with paramagnetic salt crystals, exhibit the properties of a two phase system; also dilute solutions of paramagnetic ions in water. In principle it is possible to obtain information about self‐diffusion in liquids, hydration of ions, dispersivity of solid paramagnetic material. Instrumental techniques used in the detection of the signal are described.