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

The Swiss drugmaker released data from an early-stage clinical trial for its 225Ac-PSMA-617 drug candidate that showed so-called alpha particle radioactive isotopes should work in fighting prostate cancer, 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

Clearly, the alpha particle crosses a kind of energetic barrier that normally prohibited passage, but how?

From Scientific American • Aug. 18, 2021

Each alpha particle becomes an atom of helium gas.

From Textbooks • Feb. 14, 2019

His greatest breakthrough came because he was prepared to spend immensely tedious hours sitting at a screen counting alpha particle scintillations, as they were known–the sort of work that would normally have been farmed out.

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