with the Larmorfrequenz precesses the spin of an atomic nucleus around the magnetic field.

The Larmorfrequenz is designated after the British physicist Joseph Larmor.

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Präzession des Spins

the precession of the atomic nucleus pin around an exteriorMagnetic field is comparable with a gyroscope, whose symmetry axis is not identical to the angular momentum. Since however the angular momentum is a preservation size, a further rotation must exist, the precession.

If the spin does not agree with the outside magnetic field, a Kraft affects, those the spinto a precession of the spin around the magnetic field leads.

By irradiating electromagnetic radiation with the Larmorfrequenz become lively in the atoms Niveauübergänge of the spins, so that with the varying of the frequency an absorption spectrum develops. The visible absorption line with the Larmorfrequenz becomes also resonance line or NMR line(English. Nuclear Magnetic Resonance = core-magnetic resonance) mentioned.

The Larmorfrequenz depends on the strength of the magnetic field B and that gyromagnetischem relationship γ:

<math> f = \ frac {\ gamma} {2 \ pi} \ cdot \ left| B \ right| </math> and/or. <math> \ omega = \ gamma \ cdot \ left| B \ right| </math>

Goes intothe computation the magnetic field, which prevails at the core place. This magnetic field at the core place B sets itself together from that ext and further magnetic fields , the z for external magnetic field B. B. by the electron sheath or the chemical environment to be produced.

chemical shift

is , the remaining atoms of the connection an additional magnetic field, which shifts the Larmorfrequenz characteristically, produce the atom in a chemical compound (which is called chemical shift or chemical SHIFTs).

In chemistry in nuclear spin resonance measurement this chemical shift of the Larmorfrequenz is measured, in order to make a material identification.

see also

nuclear spin Tomografie, magnet resonance, nuclear spin resonance



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