DEAN and Pound I in 1952
first suggested that a sensitive thermometer could be based on the temperature dependence of nuclear quadrupole resonanae (n.q.r.). In 1956 Kushida et al. studied the temperature dependence of n.q.r, for several substances in the range 77-350 ยฐ K. 2 The possibility of extending the range down to 15 ยฐ K was indicated by the further investigations of Vanier 3 who deduced that the accuracy to be expected of such a thermometer should be ~ + 0.005 ยฐ K at temperatures above 60 ยฐ K and ~ +0.05 ยฐ Kat20 ยฐK.
It is difficult to achieve this expected accuracy as the radiospectrometer used in the experiments was of the well known Pound-Knight type, and a long period of time was required to determine the resonance frequency, which was derived from a graphical analysis of the record of the resonance curve. For the method to be of practical value it was essential to develop a special radiospectrometer circuit which would make possible a rapid and simple measurement of n.q.r. frequency with an error of the order of 1 c/s. The present paper gives a description of an experimental arrangement, based on n.q.r., for measuring temperature.
The interaction of the quadrupole moment of a nucleus with the internal field of a crystalline solid can be represented by the scalar product of the tensors of these quantities. The interaction Hamiltonian is of the form