NMR in Chemistry: A Multinuclear Introduction by William Kemp

By William Kemp

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At the root of this discussion lies the familiar experience that a radio receiver will only receive a broadcast signal from a radio station when their frequencies are 'tuned'; tuning involves altering the capacitance of the tuning circuit, and we do this when we turn the tuning knob on the radio. 1 Radiofrequency Sources in Multinuclear NMR Crystal oscillators produce accurate and constant frequencies as a consequence of the precise capacitance of the particular crystal used. ) This fundamental frequency can be electronically multiplied to give higher overtones; these can then be modulated by another oscillator operating at audiofrequencies, so that the end product is a pair of side-bands shifted away from the original radiofrequency or its overtone by plus and minus the audiofrequency.

1 and a complete 500 MHz spectrometer is photographed at the head of the chapter. The weight of the magnet in such an installation is only about 250 kg, and the power consumption is zero (although ancillary equipment such as compressors, amplifiers, fans and the computer may need a few kilowatts). The principal running costs for the magnet are in liquid gases, particularly liquid helium. The magnet itself consists of thousands of metres of fine metal filament. 4 T, but beyond that it does not behave as a superconductor, and the core part of the solenoid must then be made of Nb 3 Sn.

3, we can only say that the magnetic moment vectors lie somewhere on the surfaces: it is a simplification (legitimate and convenient) to call them precession cones. THE FUNDAMENTAL BASIS OF MAGNETIC RESONANCE 2. 7 THE STRENGTHS OF NUCLEAR MAGNETS THE NUCLEAR MAGNETON UNIT, JlN The dimensions of nuclear magnetic dipoles (the strengths of the magnets) can be expressed as multiples of a term derived from that of the simplest nucleus - the proton; the unit used is the nuclear magneton, JlN. 8 THE MAGNETOGYRIC RATIO- 'Y An alternative constant, -y, for each nucleus can usefully be defined, combining the proportionality constant, g, with the unit of nuclear magnetic moments, the nuclear magneton, JlN, so that 'Y =KilN.

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