FAST FIELD-CYCLING NUCLEAR-MAGNETIC-RESONANCE SPECTROMETER

We describe here the design and construction of a modern, state-of-the -art nuclear magnetic resonance (NMR) field-cycling instrument. Fourie r transform NMR spectra of both liquid and solid samples can be measur ed, and spin-lattice relaxation times (T-1Z) investigated over a broad range of magnetic field strengths ranging from 0 to 2 T. The instrume nt is based upon an existing personal computer-based NMR spectrometer [C. Job, R. M. Pearson, and M. F. Brown, Rev. Sci. Instrum. 65, 3354 ( 1994)] which has been expanded into a fully computer-controlled field- cycling instrument. The magnetic field cycling is accomplished electro nically by utilizing fast switching thyristors and a storage capacitor based on the Redfield energy storage concept. Unique aspects of the d esign include the field-cycling magnet, which can reach fields as high as 2 T; the personal computer-based NMR spectrometer and associated w aveform electronics; and the use of a commercially available pulse wid th modulation switching current amplifier, having low internal power d issipation and a fast current settling time. Using this new technology T-1Z relaxation times as short as 1 ms can be readily measured. (C) 1 996 American Institute of Physics.