The sensitivity of nuclear magnetic double resonance

Abstract

The dynamics of the nuclear magnetic double resonance process for Na nuclei in a (2,0,0) position relative to a substitutional Ag+ impurity in NaCl has been studied for several Ag concentrations. The purpose was to determine experimentally the factors which limit the double resonance sensitivity. For Ag concentrations below .03 mole %, the magnetization of unperturbed Na nuclei decayed exponentially with rates proportional to the impurity concentration when an rf field at the resonance frequency of the quadrupole shifted transitions was applied. Using a new method, intermittent search field irradiation, evidence was found that the finite spin diffusion rate caused a double resonance energy transfer rate under continuous search field irradiation about 30% less than the transfer rate which would be observed if the spin diffusion were infinitely fast. A theoretical explanation of the results is given using a perturbation approach based on the concept of spin diffusion. In addition, we have studied the Na spin lattice relaxation in the completely demagnetized state as a function of impurity concentration, and found a rapid initial decrease of spin order. This was caused by cross relaxation within then nuclear spin system.