Spin is a fundamental property of elementary particles in quantum mechanics. It is a measure of intrinsic angular momentum and is not related to the actual spinning motion of a particle.
Spin half refers to particles that have a spin quantum number of 1/2. In quantum mechanics, spin is quantized, meaning it can only take on certain discrete values. The spin quantum number can be either a positive half-integer value (e.g., 1/2, 3/2, 5/2) or a negative half-integer value (e.g., -1/2, -3/2, -5/2).
Particles with spin half are called fermions. Examples of spin half particles include fundamental particles like electrons, protons, and neutrons. These particles are known as fermions because they obey Fermi-Dirac statistics, which dictate that no two identical fermions can occupy the same quantum state simultaneously.
The spin of a particle has various consequences. It affects how particles interact with each other and with external fields, and it can give rise to phenomena such as magnetism. Spin also plays a crucial role in the structure of atoms, the behavior of materials, and the formulation of quantum field theories.