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Definition of Alpha particle

Babylon English

positively charged particle made up of two protons and two neutrons, nucleus of a helium atom
Alpha particle Definition from Business & Finance Dictionaries & Glossaries
Glossary of petroleum Industry
one of the extremely small particles of an atom that is ejected from a radioactive substance (as radium or uranium) as it 'disintegrates. Alpha particles have a positive charge.
Alpha particle Definition from Science & Technology Dictionaries & Glossaries
General Chemistry Glossary
 Say it 
(42He) A particle that is commonly ejected from radioactive nuclei, consisting of two protons and two neutrons. Alpha particles are helium nuclei. Alpha particles have a mass of 6.644 655 98 × 10-27 kg or 4.001 506 1747 atomic mass units . [1998 CODATA values ]
NRC Nuclear Energy Glossary
A positively charged particle ejected spontaneously from the nuclei of some radioactive elements. It is identical to a helium nucleus that has a mass number of 4 and an electrostatic charge of +2. It has low penetrating power and a short range (a few centimeters in air). The most energetic alpha particle will generally fail to penetrate the dead layers of cells covering the skin and can be easily stopped by a sheet of paper. Alpha particles are hazardous when an alpha-emitting isotope is inside the body.
A service to the public by The U.S. Nuclear Regulatory Commission (NRC).
Technical English by wpv
The nuclei of a helium (with two neutrons and two protons each) that are discharged by radioactive decay of many heavy elements, such as uranium-238 and plutonium-239.
ASTRONOMY UNBOUND
The fast moving nucleus of a helium atom. It is emitted in one type of radioactivity known as alpha decay. The nucleus has too much energy and too many protons but finds it energetically most feasible to eject a preformed helium nucleus rather than emit a proton. The alpha particle is monoenergetic and its energy, and also the half life, uniquely identify the radionuclide. Naturally occurring alpha particle emitters are heavier than lead (Z=82). See also atomic nucleus.
Alpha particle Definition from Encyclopedia Dictionaries & Glossaries
English Wikipedia - The Free Encyclopedia
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, a. The symbol for the alpha particle is a or a2+. Because they are identical to helium nuclei, they are also sometimes written as or indicating a helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom .

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Alpha particle Definition from Entertainment & Music Dictionaries & Glossaries
English to Federation-Standard Golic Vulcan
sih-pi'gal
Alpha particle Definition from Medicine Dictionaries & Glossaries
CDC Radiological Terms
the nucleus of a helium atom, made up of two neutrons and two protons with a charge of +2. Certain radioactive nuclei emit alpha particles. Alpha particles generally carry more energy than gamma or beta particles, and deposit that energy very quickly while passing through tissue. Alpha particles can be stopped by a thin layer of light material, such as a sheet of paper, and cannot penetrate the outer, dead layer of skin. Therefore, they do not damage living tissue when outside the body. When alpha-emitting atoms are inhaled or swallowed, however, they are especially damaging because they transfer relatively large amounts of ionizing energy to living cells. See also beta particle, gamma ray, neutron, x-ray.
  
Source: Centers for Disease Control and Prevention (CDC) ( About )
Alpha particle Definition from Language, Idioms & Slang Dictionaries & Glossaries
WordNet 2.0

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