Elementary Particles
| Definition: |
Individual components of atoms, usually subatomic; subnuclear particles are usually detected only when the atomic nucleus decays and then only transiently, as most of them are unstable, often yielding pure energy without substance, i.e., radiation. |
| Notes: |
IM; includes nucleons, quarks, gluons, neutrinos, strange particles, antiparticles |
| Also Called: |
Baryons |
| Previously Indexed: |
Nuclear Physics (1966-1970) |
Elementary Particles Categories.
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Electrons - Stable elementary particles having the smallest known negative charge, present in all elements; also called negatrons. Positively charged electrons are called positrons. The numbers, energies and arrangement of electrons around atomic nuclei determine the chemical identities of elements. Beams of electrons are called CATHODE RAYS or BETA RAYS, the latter being a high-energy biproduct of nuclear decay. |
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Heavy Ions - Positively-charged atomic nuclei that have been stripped of their electrons. These particles have one or more units of electric charge and a mass exceeding that of the Helium-4 nucleus (alpha particle). |
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Mesons - Short-lived elementary particles found in cosmic radiation or produced from nuclear disintegration. Their mass is between that of protons and electrons and they can be negative, positive, or neutral. pi-Mesons (pions) are heavier than mu-mesons (muons) and are proposed for cancer radiotherapy because their capture and disintegration by matter produces powerful, but short-lived, secondary radiation. |
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Neutrons - Electrically neutral elementary particles found in all atomic nuclei except light hydrogen; the mass is equal to that of the proton and electron combined and they are unstable when isolated from the nucleus, undergoing beta decay. Slow, thermal, epithermal, and fast neutrons refer to the energy levels with which the neutrons are ejected from heavier nuclei during their decay. |
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Photons - Discrete concentrations of energy, apparently massless elementary particles, that move at the speed of light. They are the unit or quantum of electromagnetic radiation. Photons are emitted when electrons move from one energy state to another. (From Hawley's Condensed Chemical Dictionary, 11th ed) |
Elementary Particles Definitions and Terms
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