Definition

Noun: A positively charged particle that is the nucleus of a helium atom, consisting of two protons and two neutrons. It is emitted from certain radioactive isotopes during a type of radioactive decay called alpha decay.

Usage

Alpha particles are a form of ionizing radiation. They have low penetration power and can be stopped by a sheet of paper or the outer layer of human skin. However, they are highly ionizing and can cause significant damage if an alpha-emitting substance is ingested or inhaled.

Examples

• The radioactive material decayed by emitting an alpha particle.
• An alpha particle is identical to a helium-4 nucleus.
• The detector was used to measure the flux of alpha particles from the sample.

Advanced Usage

• Alpha-particle spectroscopy: A technique for measuring the energy distribution of alpha particles emitted by a source.
• Alpha emitter: A substance that undergoes radioactive decay by emitting alpha particles.
• Alpha decay: The radioactive process by which an unstable atomic nucleus loses an alpha particle.

Variants and Related Words

• Alpha radiation: The stream of alpha particles emitted from a radioactive source.
• Alpha ray (historical term): An early term for what is now understood as a stream of alpha particles.

Synonyms

• Helium nucleus (This is a direct physical synonym, as an alpha particle is precisely a helium-4 nucleus stripped of its electrons).

Related Scientific Contexts

• Rutherford's gold foil experiment: This historic experiment involved directing a beam of alpha particles at a thin gold foil, leading to the discovery of the atomic nucleus.
• Smoke detectors: Many common household smoke detectors use a tiny amount of americium-241, an alpha emitter, to ionize air and detect smoke particles.

Noun

1. a positively charged particle that is the nucleus of the helium atom; emitted from natural or radioactive isotopes