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Definition: The neutrino is an elementary particle which holds no electrical charge, travels at nearly the speed of light, and passes through ordinary matter with virtually no interaction.

Neutrinos are created as part of radioactive decay. This decay was observed in 1896 by Henri Bacquerel, when he noted that certain atoms seem to emit electrons (a process known as beta decay). In 1930, Wolfgang Pauli proposed an explanation for where these electrons could have come from without violating conservation laws, but it involved the presence of a very light, uncharged particle emitted simultaneously during the decay. Neutrinos are produced through radioactive interactions, such as solar fusion, supernovae, radioactive decay, and when cosmic rays collide with the Earth's atmosphere.

It was Enrico Fermi who developed a more complete theory of neutrino interactions and who coined the term neutrino for these particles. A group of researchers discovered the neutrino in 1956, a finding which later earned them the 1995 Nobel Prize in Physics.

There are actually three types of neutrino: electron neutrino, muon neutrino, and tau neutrino. These names come from the their "partner particle" under the Standard Model of particle physics. The muon neutrino was discovered in 1962 (and earned a Nobel Prize in 1988, 7 years before the earlier discovery of the electron neutrino earned one.)

Early predictions indicated that the neutrino may have had no mass, but later examinations have indicated that it has a very small amount of mass, but not zero mass. The neutrino has a half-integer spin, so it is a fermion. It is an electronically neutral lepton, so it interacts through neither the strong nor electromagnetic forces, but only through the weak interaction.

Pronunciation: new-tree-no
Also Known As:
  • Electron Neutrino
  • Muon Neutrino
  • Tau Neutrino
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