Spin
What it is
Spin is the amount of angular momentum associated with a subatomic particle
or nucleus. Spin is measured in multiples of a unit called the Dirac h, or h-bar
which is equal to the Planck constant divided by 2 pi.
Particles like electrons, neutrons, and protons, which possess spin in multiples
of .5 are called Fermions, and particles like pions and photons which possess
integer multiples are called bosons. The spin (More correctly, the total angular
momentum) of nuclei more complex than the proton is the vector sum of the
orbital angular momentum and intrinsic spins of the constituent nucleons. For
nuclei of even mass number, the multiple is an integer; for those of odd mass
number, the multiple is a half-integer. All nuclei with even numbers of neutrons
and protons have spin zero in their ground states.
The assertion that no two electrons in an atom could occupy the same state or
configuration, at the same time, was proposed in 1925 by Wolfgang
Pauli(1900-1958) to account for the observed patterns of light emission from
atoms. This exclusion principle subsequently was generalized to include
particles other than just the electron.
Subatomic particles fall into two classes, based on their statistical
behavior. Fermions obey the Pauli exclusion principle and bosons do not. In a
closed system, such as an atom, fermions are distributed so that a given state
is occupied by only one at a time. Four quantum numbers are used to specify the
various states that a fermion can assume.
History
Pieter Zeeman (1865-1943) received the Nobel prize in 1902 for his discovery
of the "Zeeman effect", the splitting of single spectral lines of an
emission spectrum into three or more polarized components when the radiation
source is in a magnetic field.
In 1922 Otto Stern (1888-1969) and Gerlach discovered that a beam of sliver atoms splits in a
magnetic field.
In 1925 George Eugene Uhlenbeck (1900-1988) and Samuel Abraham Goudsmit
(1902-1978) proposed that the electron has an intrinsic
angular momentum ( spin).
In 1927 Wolfgang Pauli(1900-1958) introduces spin into quantum mechanics to
explain the electron configuration of atoms.
Common equations
Units
Units and half units of integer. (0, 1/2, 1, 3/2, 2, etc.)
Editorial comments
Note that spin (Quantum angular momentum) plays a very important role in
controlling man's perception of the relationship between discrete objects and
space. Although any number of integer spin objects (Bosons) can be assigned to a
particular point in space, half integer spin objects require a more complex
topology. Spin seems to determine the configuration of objects (Topology), and
topology seems to determine space.