neutron

American  

[noo-tron, nyoo-] / ˈnu trɒn, ˈnyu- /

noun

Physics.

1. 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. n

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neutron British  

/ ˈnjuːtrɒn /

noun

1. 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

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neutron Scientific  

/ no̅o̅′trŏn′ /

1. 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 1.0×10 ³ 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.

2. See Table at subatomic particle

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neutron Cultural  

1. 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.

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Etymology

Origin of neutron

First recorded in 1920–25; neutr(o)- + -on ¹

Explanation

The nucleus of an atom includes a proton, which has a positive charge, and a neutron, which has no charge, or is "neutral." The hydrogen atom is the only atom without a neutron. The basis for the word neutron is both "neutral" and the suffix "-on," which probably comes from the Greek ión, "to go." The word ion first appeared in English in 1834, and neutron appeared in 1921, to represent the neutral part of an atom. Don't let the "neutral" part fool you, though — a neutron bomb, while "smaller" than other nuclear weapons, is still capable of mass destruction, as it emits more radiation, causing a wider sweep of damage to life.

Example Sentences

These p-nuclei cannot be produced through neutron capture.

From Science Daily • Apr. 14, 2026

Researchers measured the properties of a magnetic crystal using a process called neutron scattering, where a beam of neutrons passes through a sample.

From Barron's • Mar. 26, 2026

Researchers had already ruled out stripped stars and neutron stars because observations did not match theoretical predictions.

From Science Daily • Mar. 25, 2026

The observation suggests that current theoretical explanations are incomplete and that scientists need a more sophisticated framework to explain why some decays release one neutron while others release two.

From Science Daily • Mar. 13, 2026

To this day, neutron therapy as pioneered by the cyclotroneers in 1938 remains an important part of the arsenal against certain cancers, including those of the prostate and salivary glands.

From "Big Science" by Michael Hiltzik