Many atoms have nuclei that can behave as though they were tiny magnets. These nuclei are said to have magnetic moments. The strength of the magnetic moment is unique for different nuclei and may serve as a distinguishing characteristic of a nucleus. The tiny nuclear magnets can be manipulated, like any magnet, by applying external magnetic fields.

When a material is placed in a constant magnetic field the nuclei of the atoms will tend to line up with the field in the same way that a compass needle lines up with the Earth's magnetic field. At equilibrium there will be a small majority of nuclei lined up with the field. The magnetic moments of different nuclei can then be selectively manipulated by applying time varying magnetic fields of just the right frequency and durration.

It is possible for example to rotate the magnetic moments of the Hydrogen nuclei in the material so that they become perpendicular to the constant magnetic field. The magnetic moments will then start to rotate in unison, producing a time varying magnetic field that can induce a detectable voltage in a coil. For a given constant magnetic field stregnth the exact frequency at which the magnetic moments rotate will depend upon their environment. The same type nucleus will rotate at slightly different frequencies in different molecules. This allows the presence of different molecules to be detected and it is one of the things that makes NMR so useful.

For a simple, nontechnical introduction to NMR see: A Layman's Introduction to Nuclear Magnetic Resonance

For a more technical introduction geared toward chemists see: The Basics of NMR

NMR has the following benefits:

• Gives you information about matter below the surface of a sample.
• Does not alter the structure of a sample.
• Not harmful to living things, unlike xrays and electron beams.
• Can be used to study the diffusion and dynamics of atoms and molecules in a sample.
• Usually does not require special sample preparation.
• Can be used as the basis for a quantum computer.
• The most accurate way to measure magnetic fields.

A team at the California Institute of Technology has used MRI to observe enzyme activity in a developing frog embryo. The resolution can image individual cells. See: MRI Scans for Enzyme Activity

Researchers at the Georgia Institute of Technology are using MRI to study how wet carpets dry in order to improve the manufacturing process. They are also studying the way different fabrics wick moisture away from the skin. See: MRI For Carpets & Fabrics

A relatively new field of research called Quantum Computing offers the potential for creating computers vastly more powerful than anything imaginable with current technology. Several researchers have used NMR to implement rudimentary quantum computers. Researchers at IBM have created the most advanced NMR quantum computer to date. See: IBM-Led Team Unveils Most-Advanced Quantum Computer

NMR is increasingly being used in biochemistry. See: Why NMR is attracting drug designers

NMR Resources