alpha particle

American  

noun

Physics.

1. a positively charged particle consisting of two protons and two neutrons, emitted in radioactive decay or nuclear fission; the nucleus of a helium atom.

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alpha particle British  

noun

1. a helium-4 nucleus, containing two neutrons and two protons, emitted during some radioactive transformations

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alpha particle Scientific  

1. A positively charged particle that consists of two protons and two neutrons bound together. It is emitted by an atomic nucleus undergoing radioactive decay and is identical to the nucleus of a helium atom. Because of their relatively large mass, alpha particles are the slowest and least penetrating forms of nuclear radiation. They can be stopped by a piece of paper.

2. See more at radioactive decay

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Etymology

Origin of alpha particle

First recorded in 1900–05

Example Sentences

See Examples For:

alpha particle

Pluvicto carries a beta particle that travels for a longer range but is less lethal, while the new therapy uses an alpha particle that is more lethal but travels shorter distances, the analyst says.

From The Wall Street Journal ● Jun. 2, 2026

It took 23 measurements with an instrument called an alpha particle X-ray spectrometer.

From BBC ● Aug. 21, 2024

Added to this was the challenge of procuring radioactive curium-244, an alpha particle source that is central to APXS—and that Vadawale notes is “available only from Russia.”

From Scientific American ● Jul. 13, 2023

Only later—when the scientists comb through the raw data and match every detected alpha particle to a specific element in the decay chain—can they reconstruct which element they initially created.

From Science Magazine ● Jan. 30, 2019

When he accelerated an alpha particle through the chamber to seed his make-believe clouds, it left a visible trail–like the contrails of a passing airliner.

From "A Short History of Nearly Everything" by Bill Bryson