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[noo-tron, nyoo-] /ˈnu trɒn, ˈnyu-/
noun, Physics.
an elementary particle having no charge, mass slightly greater than that of a proton, and spin of ½: a constituent of the nuclei of all atoms except those of hydrogen. Symbol: n.
1920-25; neutr(o)- + -on1 Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for neutrons
  • To produce power, the fuel rods must first be bombarded with neutrons.
  • Quarks are the elementary building blocks of positively charged protons and neutral neutrons, which make up atomic cores.
  • Regular visible matter is made up of protons, neutrons, and other subatomic particles collectively called baryons.
  • Later that same year, after bombarding uranium with neutrons, they found barium.
  • They had been bombarding natural uranium with slow neutrons.
  • But some theories suggest neutron stars could squish down even further by converting their neutrons to exotic types of matter.
  • From interacting protons and electrons, you can get neutrons.
  • The energy crushed the capsule instantly, causing it to spew a shower of neutrons.
  • When one of those neutrons hits a uranium atom, it also initiates fission into lighter elements, releasing more neutrons.
  • As the universe expanded and cooled, some of these particles merged to form neutrons and protons.
British Dictionary definitions for neutrons


(physics) a neutral elementary particle with a rest mass of 1.674 92716 × 10–27 kilogram and spin 1/2; classified as a baryon. In the nucleus of an atom it is stable, but when free it decays
Word Origin
C20: from neutral, on the model of electron
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for neutrons



"electrically neuter particle of the atom," 1921, coined by U.S. chemist William D. Harkins (1873-1951) from neutral (adj.) + -on. First record of neutron bomb is from 1960. Neutron star attested from 1934, originally hypothetical; so called because it would be composed of neutrons.

Online Etymology Dictionary, © 2010 Douglas Harper
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neutrons in Medicine

neutron neu·tron (nōō'trŏn', nyōō'-)
An electrically neutral subatomic particle in the baryon family, having a mass 1,839 times that of the electron, stable when bound in an atomic nucleus, and having a mean lifetime of approximately 1.0×103 seconds as a free particle. It and the proton form nearly the entire mass of atomic nuclei.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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neutrons in Science
An electrically neutral subatomic particle in the baryon family, having a mass of 1.674 × 10-24 grams (1,838 times that of the electron and slightly greater than that of the proton). Neutrons are part of the nucleus of all atoms, except hydrogen, and have a mean lifetime of approximately 1.0×103 seconds as free particles. They consist of a triplet of quarks, including two down quarks and one up quark, bound together by gluons. In radioactive atoms, excess neutrons are converted to protons by beta decay. Beams of neutrons from nuclear reactors are used to bombard the atoms of various elements to produce fission and other nuclear reactions and to determine the atomic arrangements in molecules. See Table at subatomic particle.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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neutrons in Culture

neutron definition

An elementary particle without an electrical charge; one of the building blocks of the nucleus of the atom. A neutron has about the same mass as a proton.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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