Zero-field NMR and NQR spectrometer

Abstract

In comparison to high-field NMR, zero-field techniques offer advantages in terms of spectral interpretability in studies of polycrystalline or amorphous solids. This article describes a technique and apparatus for time-domain measurements of nuclear magnetism in the absence of applied fields (Fourier transform zero-field NMR and NQR). Magnetic field cycling and high field detection are employed to enhance sensitivity. The field cycling is accomplished with an air-driven shuttle system which moves the sample between regions of high and low magnetic field, in combination with switchable electromagnets in the low-field region. Sudden field steps or pulses are used to initiate coherent nuclear spin evolution in zero field and to monitor such evolution as a function of time. Experimental results are shown and analyzed. Possible variations on the basic method are described and their relative advantages are discussed.