Neutrino
Neutrino, an elementary particle that has no electric charge. Physicists believe that neutrinos have either an extremely small mass or no mass at all. Neutrinos are produced by the decay of subatomic particles in certain types of radioactivity and nuclear reactions. The nuclear fusion of hydrogen in the sun and other stars produces large numbers of neutrinos.
Neutrinos seldom interact with other particles; consequently they can pass unaffected through large solid objects—including the earth itself. The only type of interaction that does takes place between neutrinos and other particles is called the weak interaction. The study of neutrinos and the weak interaction has helped physicists in developing theories that describe the fundamental properties of matter.
The existence of the neutrino was proposed in 1930 by Wolfgang Pauli, an Austrian-American physicist. He suggested that the emission of this particle would account for the apparent loss of energy observed in a type of radioactivity known as beta decay. In the early 1930's, Enrico Fermi, an Italian-American physicist, gave the neutrino its name and worked out a theory describing the neutrino and its interaction with other particles. Neutrinos were first detected in 1956 by two American physicists, C. L. Cowan and Frederick Reines, and their collaborators. Three kinds of neutrinos are now known. Each kind has a corresponding antineutrino.