neutron

[noo-tron, nyoo-]
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

Origin:
1920–25; neutr(o)- + -on1

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World English Dictionary
neutron (ˈnjuːtrɒn)
 
n
physics a neutral elementary particle with a rest mass of 1.674 92716 × 10--27 kilogram and spin ½; classified as a baryon. In the nucleus of an atom it is stable, but when free it decays
 
[C20: from neutral, on the model of electron]

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Etymonline
Word Origin & History

neutron
1921, coined by W.D. Harkins of Chicago from neutr(al) + -on, as in electron. First record of neutron bomb is from 1960.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

neutron neu·tron (nōō'trŏn', nyōō'-)
n.
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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American Heritage
Science Dictionary
neutron   (n'trŏn')  Pronunciation Key 
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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American Heritage
Cultural Dictionary

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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Example sentences
The mysterious source of this antimatter has now been discovered -- stars
  getting ripped apart by neutron stars and black holes.
If this is designed for neutron protection, it is poorly done.
The object may well be a superdense neutron star, as predicted by theory,
In this case, one neutron in the nucleus breaks apart.
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