7.3 : Atomic Nuclei: Nuclear Magnetic Moment

All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B₀) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a proton, has an value of ½ and two possible orientations. The orientation aligned with the field (called spin +½, spin-up, or α) has lower energy than the orientation aligned against the field (called spin −½, spin-down, or β).