Neutrino
Based on theoretical considerations concerning events that occur spontaneously in the nuclei of atoms, the physicist, Wolfgang Pauli (1900-1958),[1] in 1930, postulated a new fundamental particle of matter, subsequently (1935) named by the physicist, Enrico Fermi (1901-1954),[2] the neutrino ("little neutral one", in Fermi's Italian). The neutrino is an electrically uncharged particle, initially conceived of as associated with the negatively electrically charged particle, the electron, specifically an electron that certain unstable atoms' nuclei generate and emit during a certain type of radioactive emission called beta decay, which occurs spontaneously in certain varieties (isotopes) of certain of Earth's naturally-occurring chemical elements.[3] Initially the electron-accompanying neutrino was presumed to have no mass.
Physicists subsequently confirmed the existence of the 'electron neutrino' and provided evidence that it has a "vanishingly small" but finite mass. Physicists have also provided evidence of two additional types, or 'flavors', of neutrinos, the muon neutrino, associated with muon particles, and the tau neutrino, asocciated with tau particles, and they provided evidence that an antineutrino exists for each of the three flavors of neutrinos.[4]
The study of neutrinos has begun to reveal important information about the nature of the universe. This article will discuss what physicists currently know about neutrinos, and to some extent, how they came to that knowledge, its implications regarding the nature of atoms and the universe, and its applications for discovery and for human use.
Background
| The neutrinos appear to constitute by number of species not less than one quarter of the particles which make the world, and even half of the stable ones. By number of particles in the Universe they are perhaps second only to photons. |
At the time of Pauli's postulated existence of the neutrino, physicists had already discovered that atoms, previously thought of as homogeneous and indivisible, consisted of sub-particles, called subatomic particles, specifically, protons and neutrons, localized in a center-of-the-atom nucleus, the major location of the atoms' mass, and electrons, by comparison tiny, surrounding the nucleus. The protons each carried a unit of positive electric charge and the electrons, equal in number to the number of protons, each carried a unit of negative electric charge, rendering the atom as a whole electrically neutral, inasmuch as the neutron itself carried no electric charge.
| Of all the things that make the universe, the commonest and weirdest are neutrinos. Able to travel through the earth like a bullet through a bank of fog, they are so shy that half a century after their discovery we still know less about them than all the other varieties of matter that have ever been seen. |
They had also discovered that some atoms were unstable, in that their nuclei might emit energy (electromagnetic and kinetic) and one or more subatomic particles, a process called radioactivity.
Basing his thinking on the widely accepted law of conservation of energy, Pauli postulated the existence of an electron-associated, presumably massless, neutrino, postulated in order to reconcile an observed discrepancy between the energy emitted from the nucleus during the radioactive process called 'beta decay' — energy too small — and the energy change of the nucleus itself, the missing energy, the energy lost by the nucleus during the beta decay process, carried off by the postulated chargeless neutrino particle.[6]
References
- ↑ Biography of Wolfgang Pauli on the Nobel Prize website.
- ↑ Biography of Enrico Fermi on the Nobel Prize website.
- ↑ 3.0 3.1 Close F. (2010) Neutrino. Oxford: Oxford University Press. ISBN 9780199574599. | Google books preview. Cite error: Invalid
<ref>tag; name "close2010" defined multiple times with different content - ↑ Franklin A. (2001) Are There Really Neutrinos? An Evidential History. Cambridge, MA: Perseus. ISBN 0738202657. |Google Books preview.
- ↑ Anicin IV. (2005) The Neutrino: Its past present and future. arXivPhysics/0503172v1. Downloadable PDF. | Author: Faculty of Physics, University of Belgrade.
- ↑ The Story of the Neutrino. NuMI-MINOS Homepage. Fermi National Accelerator Laboratory. | NuMI = Neutrino at Main Injector, a FermiLab project to generate an intense beam of neutrinos for study; MINOS = Main Injector Neutrino Oscillation Search, experiments to study the phenomenon of 'neutrino oscillations'.