Nuclear Quadrupole Resonance Thermometry

The technique of Nuclear Quadrupole Resonance thermometry is described. It is shown that the N.Q.R. thermometer exhibits unique properties of sensitivity, range, and reproducibility that are all desirable qualities for a temperature standard. The response to temperature is a unique characteristic of the working substance, which in this case is KClO 3 . Experimentally, the center frequency of the absorption line of Cl 35 in pure samples of KClO 3 at 77 °K is reproducible to approximately 2 Hz. This corresponds to an absolute accuracy of better than ± 0.001 °K. The purity of the samples is achieved by recrystallization of commercial reagents. The range of the thermometer extends from 10 °K to approximately 450 °K. A description of a simple system which locks an oscillator to the N.Q.R. absorption line is given. A new method of determining accurately the frequency of the center of the line using magnetic field broadening is also described. With this technique a sensitivity of ± 0.0002 °K is expected. In line with these results, evaluation of a thermometer based on the temperature dependence of the nuclear magnetic resonance frequency in antiferromagnetic salts is made.