A study of the super-regenerative detection of nuclear quadrupole resonance

Abstract

When the spin, I, of an atomic nucleus is greater than one-half it has an electric quadrupole moment, Q. The quadrupole moment is a measure of the deviation of the nuclear charge from spherical symmetry. In atoms and molecules nuclei are embedded in an electronic cloud. When the electrons and other charges outside a particular quadrupole nucleus have a non-spherical charge distribution, there is an interaction between the nuclear field and external field. A nucleus possessing a quadrupole moment situated in an inhomogeneous electric field possesses a potential energy; the possible orientations of the spin axis of the nucleus in a molecule, relative to the molecular axis, are quantised. Thus there will be a number of different energy states. In solids, direct transitions between levels corresponding to different nuclear orientations can be observed by means of pure nuclear quadrupole resonance spectroscopy. The frequencies observed are generally in the ratio frequency region. The theory and applications of nuclear quadrupole resonance have been the subject of a number of reviews. (1,2,3,4,5,6).