A Pulsed NMR System for Nuclear Thermometry Below 2 K

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Abstract
A pulsed NMR system for platinum nuclear spin thermometry and for measurements of the nuclear spin‐lattice relaxation time τ1 has been developed. The nuclear free precession signal is detected with a fast linear detector and an RC integrator. The τ1 measurements were performed by the transient recovery method with the aid of automated circuitry multiplexing of the linear detector output into four separate integrators. The thermometer was tested between 10 mK and 2 K using a powdered platinum sample. Within the experimental accuracy of about 2% the amplitude of the nuclear free precession signal was found to be proportional to 1/T. The thermometer could be calibrated with the aid of the Korringa relation τ1T=κ, with κ=29.6 msec K. Thermal equilibrium problems of the τ1 measurements are discussed in detail.

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