neutron

American  

[noo-tron, nyoo-] / ˈnu trɒn, ˈnju- /

noun

Physics.

neutrons plural

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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Other Word Forms

Noun Inflected Forms

• neutrons
  plural

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

Many of the chemical elements found throughout the universe are forged during extreme cosmic events, including supernova explosions and neutron star mergers.

From Science Daily • Jul. 8, 2026

Created by an international team at GSI/FAIR, the machine learning model allows scientists to simulate the complex nuclear reactions that occur during neutron star mergers and other violent stellar events far more efficiently than before.

From Science Daily • Jul. 8, 2026

Astronomers have, for the first time, observed the birth of a magnetar, an extremely magnetic, rapidly spinning type of neutron star.

From Science Daily • Jul. 6, 2026

Because this disk was likely tilted relative to the magnetar's spin, Einstein's theory predicts that the rapidly spinning neutron star would drag the surrounding fabric of space-time with it, producing a phenomenon called Lense-Thirring precession.

From Science Daily • Jul. 6, 2026

In K-capture, the nucleus absorbs one of the two electrons from its innermost electron “shell”— the “K” shell—thereby transforming a nuclear proton into a neutron.

From "Big Science" by Michael Hiltzik