# Article

# Article

- Physics
- Atomic and molecular physics
- Spin (quantum mechanics)

- Physics
- Elementary particle physics
- Spin (quantum mechanics)

- Physics
- Nuclear physics
- Spin (quantum mechanics)

- Physics
- Quantum mechanics
- Spin (quantum mechanics)

# Spin (quantum mechanics)

Article By:

**Goebel, Charles J. **Department of Physics, University of Wisconsin, Madison, Wisconsin.

Last reviewed:June 2020

DOI:https://doi.org/10.1036/1097-8542.645500

**The intrinsic angular momentum of a particle.** It is that part of the angular momentum of a particle which exists even when the particle is at rest, as distinguished from the orbital angular momentum. The total angular momentum of a particle is the sum of its spin and its orbital angular momentum resulting from its translational motion. The general properties of angular momentum in quantum mechanics imply that spin is quantized in half integral multiples of ℏ (*h*/2π, where *h* is Planck's constant); orbital angular momentum is restricted to half *even* integral multiples of ℏ. A particle is said to have spin $\raisebox{1ex}{$\text{3}$}\!\left/ \!\raisebox{-1ex}{$\sqrt{\text{2}}$}\right.$, meaning that its spin angular momentum is $\raisebox{1ex}{$\text{3}$}\!\left/ \!\raisebox{-1ex}{$\sqrt{\text{2}}$}\right.$ *h*. * See also: ***Angular momentum**

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