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Spins

Spins in magnetisms

In physics, the own angular momentum of individual particles is called "spin" (in English "rotation"). This is a quantum mechanical theory. From a physical point of view, however, the abstract concept of rotating particles does not exactly correspond to reality. Rather, spins are to be understood as an analogy to processes with similar properties (such as the orbital angular momentum). Stephen Hawking used an arrow analogy to explain the angular momentum of particles:

  • "A particle with spin 0 is a point: It looks the same from all directions. A particle with spin 1, on the other hand, is like an arrow: it looks different from different directions. The particle only looks the same again with a complete revolution (360 degrees). A particle with spin 2 is like an arrow with a tip at each end. It looks the same after half a turn (180 degrees). "
Spin is one of the basic assumptions in numerous natural sciences, such as magnetism and chemistry.

Calculation of spins

In 1925, the physicists Goudsmit and Uhlenbeck first used the term “spin” to explain the splitting of spectral lines during an experiment. Since a spin describes the angular momentum in relation to a particle's own body axis, this process can be mapped as an axial vector. According to the spin statistics theorem, fermions have a half-integer and bosons an integer spin quantum number s. The spin therefore always (also in magnetism) represents an integral or half-fold multiple of Planck’s quantum of action ℏ. Accordingly, the following applies to the calculation of spin quantum numbers for different elementary particles:

  • fermions:
electron, neutrino, quarks → 1/2 ℏ

Supersymmetric particles → 3/2 ℏ

  • Bosons:
Higgs boson → 0

Photon, Gluon, W-Boson, Z-Boson → 1ℏ

Graviton → 2ℏ

To determine the total spin value from larger systems such as protons, neutrons, atomic nuclei, atoms or molecules, the spins of the individual particles have to be added.

Spins and their importance for science

Today spins play an important role in many areas of research and technology - from magnetism to medical examinations. Considerations about the quantum mechanical orbital momentum contribute significantly to the explanation of the magnetic moment of an atomic particle. Depending on the type of spin, a particle contains different amounts of energy in a magnetic field. Since there is a magnetic interaction between electron spins and nuclear spins, special spectral lines are created. Their behavior can be optimally used for electron spin resonance or magnetic resonance imaging (also called magnetic resonance imaging, MRT for short).