nucleaire magnetische resonantie

The small majority of nuclear spins aligned in the lower energy state represents the excess population.

As the spins precess about the B₀ field at the Larmor frequency, ω, the sum of their magnetic moments results in a net magnetization about the z axis.

When a pulse or a short burst of radio waves is applied along the x axis, the nuclei absorb energy corresponding to their Larmor frequency.

The coupling of frequencies causes resonance and flips the nuclear spins of the excess population from the lower to the higher energy state, shifting the net magnetization towards the y axis.

On withdrawing the radiation pulse, the nuclear spins lose the absorbed energy. The net magnetization vector shifts back to the z axis, and equilibrium is established.

All NMR-active nuclei exhibit nuclear magnetic resonance, which forms the basis of NMR spectroscopy and imaging.