Accurate measurement of NMR amplitudes using a computer-controlled wide line cw nuclear double resonance spectrometer

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Abstract
A computer-controlled cw nuclear magnetic double-resonance spectrometer, designed for studying the spin-lattice relaxation of quadrupolar nuclei in single crystals, is described. Resonances are detected by a Robinson spectrometer using a technique involving sinusoidal field modulation in conjunction with first and second harmonic phase-sensitive detection. The output of the first harmonic detector provides an error signal, which is used to ''lock'' the spectrometer to the center of the resonance. The output of the second harmonic detector is used as the measure of NMR amplitude. Comprehensive tests have shown that the amplitudes of weak NMR signals can be compared with an accuracy of better than +/-0.1%. Numerous precautions to obtain such accuracy are discussed.