Nuclear Magnetic Resonance

Nuclear magnetic resonance (NMR) is the quantum-mechanical phenomenon in which atomic nuclei with non-zero spin absorb and re-emit electromagnetic radiation when placed in a strong static magnetic field. The resonance frequency — the Larmor frequency — is determined by the gyromagnetic ratio of the nucleus and the strength of the applied field, making NMR exquisitely sensitive to chemical environment through the chemical shift. Discovered independently by Felix Bloch and Edward Mills Purcell in 1946, NMR began as a tool for probing molecular structure in chemistry and became the physical basis for magnetic resonance imaging when researchers realized that spatially encoded NMR signals could reconstruct images of macroscopic objects. The same physics that reveals the bonding structure of a protein also images a beating heart — a scale span of ten orders of magnitude unified by a single quantum effect.