CENCO® Nuclear Magnetic Resonance without Oscilloscope

Comprehensive and economical apparatus set.

The sample, contained in a small plastic vial, is placed inside the coil of a boundary R.F. oscillator. Both are then placed in the field of a strong permanent magnet and the R.F. oscillator is turned on. At a certain R.F. frequency determined by the nuclear species present in the sample and the strength of the fixed magnetic field, the magnetic moments of the nuclei in the sample resonate with the fields and absorb energy from the R.F. oscillator by quantum transitions of the nuclear magnetic moment. This causes a large change of the oscillator's amplitude, which can be observed on an oscilloscope. The apparatus set includes a large permanent magnet with flat pole pieces and soft iron pads to improve the homogeneity of the field to better than 5 p.p.m. The field strength at the center of the gap is about 0.5T. Helmholtz coils surround the pole pieces and a scan control unit supplies an adjustable a.c. signal to the Helmholtz coils to scan the fixed magnetic field through a narrow range. The oscillator control unit carries coarse and fine frequency adjustments and produces an R.F. signal of very high frequency stability. The frequency is measured by an included frequency counter. When the frequency is adjusted so that the resonance lies within the scan range of the fixed field, two resonance signals are seen on an oscilloscope for each scan cycle. Fine adjustment of the frequency, R.F. amplitude, and scan range allows the signals to be symmetric „ for this use a Lissajous figure method is most effective. The fixed field strength and the fixed frequency now define the resonance condition for the sample.