alpha particle

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al·pha par·ti·cle (α),

a particle consisting of two neutrons and two protons, with a positive charge (2e+); emitted energetically from the nuclei of unstable isotopes of high atomic number (elements of mass number from 82 up); identical to the helium nucleus.
Synonym(s): alpha ray

alpha particle

a particle emitted from an atom during one kind of radioactive decay. It consists of two protons and two neutrons, the equivalent of a helium nucleus. Ordinarily, alpha particles are a weak form of radiation with a short range and are not considered hazardous unless inhaled or ingested.

alpha particle

A radioactive decay product, 4He nucleus, composed of two protons and two neutrons (the same as the nucleus of a helium-4 atom) with marked ionising capacity (3–9 million electron-volts) but a short range (3–9 cm in air, 25–40 µm in water/soft tissue), derived from alpha decay, which are created by the decay of a radioactive material or from nuclear bombardment. APs arising from radon, uranium and plutonium “daughters” are implicated in inhalation-induced neoplasia of the respiratory tract.

While alpha particles are highly tissue-destructive, they travel only short distances and are blocked by a thick piece of paper or skin; an AP is essentially a helium atom nucleus and generally carries more energy than gamma or beta radiation, depositing that energy very quickly while passing through tissue. Alpha particles cannot penetrate the outer, dead layer of skin; they therefore do not cause damage to living tissue when outside the body. When inhaled or ingested, however, APs are especially damaging because they transfer relatively large amounts of ionising energy to living cells.

alpha particle

a type of subatomic particle found in the atomic nucleus.

al·pha par·ti·cle

(alfă pahrti-kĕl)
A particle consisting of two neutrons and two protons, with a positive charge; emitted energetically from the nuclei of unstable isotopes of mass number 82 and up.
Synonym(s): alpha ray.
References in periodicals archive ?
Physicists had not yet straightened out the matter in detail, but in 1915 the American chemist William Draper Harkins (1875-1951) noted that the helium nucleus was not quite four times as massive as the hydrogen nucleus.
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The researchers meticulously recorded the emission of four alpha-particles, each a helium nucleus with two protons and two neutrons.
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The tardy antiprotons apparently get trapped in relatively long-lived atomic states, in which an antiproton temporarily replaces one of the two electrons bound to a helium nucleus.
This nucleaus regains internal quietude by immediately ejecting a fast-moving proton or neutron and becoming a tritium nucleus (a radioactive, triple-heavy hydrogen isotope) or a neutron-deficient helium nucleus.