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How does nuclear magnetic resonance measure nuclear magnetic moments?

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magnetic resonance Figure 1: Precession of a magnetic dipole moment μ in the presence of a constant field H and a rotating field H′ (see text)

Nuclear magnetic resonance (NMR) measures nuclear magnetic moments by exploiting the behavior of atomic nuclei that possess an unpaired proton or neutron, which causes them to act like tiny magnets.1

When these nuclei are placed in a strong, stationary magnetic field, the field exerts a torque that causes the nuclear magnetic moments to undergo Larmor precession, tracing out a cone-shaped path at a specific natural frequency.12

To measure these moments, a weak, oscillating radio wave is applied to the sample. When the frequency of this oscillating field matches the natural precession frequency of the nuclei, the system enters a state of resonance. During this state, the nuclei absorb energy from the radio wave, causing their orientation and magnetic energy state to change. By measuring the energy absorbed or liberated during these transitions—often by varying the frequency of the field and recording the resulting spectral peaks—scientists can determine the characteristic magnetic behavior of specific nuclei.12