Atomic Nuclei: Nuclear Spin

All atomic particles possess intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of one-half.

Unlike electrons, protons and neutrons in nuclei may have higher spins, but the values are always half-integers.

All particles in a nucleus contribute to the overall nuclear spin, I.

In nuclei, protons pair with protons, and neutrons pair with neutrons. Paired particles contribute zero net spin to the nucleus. So, a nucleus with nonzero spin has at least one unpaired particle.

If the number of either protons or neutrons is odd, the nuclear spin is a half-integer because of the unpaired proton or neutron.

Likewise, if both the number of neutrons and protons is odd, the nuclear spin is a nonzero integer.

Even though all nuclei with nonzero spins are NMR-active, spin-half nuclei — with spherical charge distribution and symmetric fields — are preferred for NMR studies.