Nuclear magnetic resonance at low temperatures

Abstract

Investigations have been made on nuclear paramagnetism at low temperatures by the radiofrequency resonance absorption method. In measurements on solid hydrogen it has been found that there are considerable changes in the width of the resonance line with change of temperature. These effects are related to changes in the nature of the molecular motions and the state of the molecular order. A number of experiments have been made on nuclear spin-lattice relaxation in different substances. It has been shown that in ionic crystals the nuclear relaxation is greatly affected by the presence of paramagnetic impurities. The nuclear relaxation time in metals has been found to be in reasonable agreement with theoretical predictions. Measurements have been extended to temperatures below 1 ° K, and the possibility of cooling the nuclear spin system by adiabatic demagnetization has been verified. The results for nuclear spin-lattice relaxation are considered in relation to the possible applications of nuclear paramagnetism in the region of very low temperatures.