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

Depending on conditions, the collapse can leave behind either a neutron star or a black hole.

From Science Daily • May 27, 2026

Similar effects occur throughout the universe, including inside the Sun and during neutron star mergers.

From Science Daily • May 26, 2026

At the same time, the gamma-ray and neutron spectrometer team gathered measurements that can now be compared with decades of existing Mars data.

From Science Daily • May 26, 2026

The stock barely reacted to results of an experiment with the Cleveland Clinic at the start of the month, and didn’t budge when IBM released data from a neutron scattering experiment in March.

From Barron's • May 22, 2026

Then came what he called the moment of truth: they brought the sample to the thirty-seven-inch cyclotron, placed it in a neutron beam, and waited for their detector to announce the kicks that indicated fission.

From "Big Science" by Michael Hiltzik