Apparatus for Nuclear Magnetic Resonance

Apparatus and procedures are described for the high‐resolution measurement of resonance shifts and for the observation of broad line shapes. Included are a discussion of magnet design and a summary of empirical results obtained in the construction and field homogenization of two large permanent magnets. Narrow, complex resonance lines, with components separated by as little as a milligauss, are resolved by a combination of homogeneous applied magnetic field, small samples, and slow‐sweep field modulation. Broad absorption line shapes are plotted at fixed frequency by a system incorporating a regenerative oscillator, a narrow band amplifier, a recording potentiometer, and an electronic control for varying the applied magnetic field linearly in time. A simple cryostat provides stable temperatures from 85° to 500°K. In the case of samples with short spin‐lattice relaxation times, such as the metals, improved signal‐to‐noise ratios are obtained by adjusting the oscillator to super‐regenerative operation and observing the frequency modulation associated with the dispersive component of the resonance.