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[poz-i-troh-nee-uh m] /ˌpɒz ɪˈtroʊ ni əm/
noun, Physics.
a short-lived atomic system consisting of a positron and an electron bound together.
1945; positron + -ium, coined by A. E. Ruark (born 1899), U.S. physicist Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for positronium
  • The atoms, called positronium, consist of an electron and positron orbiting each other.
  • Positron and positronium annihilation in low-dielectric-constant films studied by a pulsed positron beam.
British Dictionary definitions for positronium


(physics) a short-lived entity consisting of a positron and an electron bound together. It decays by annihilation to produce two or three photons
Word Origin
C20: from positron + -ium
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Encyclopedia Article for positronium

short-lived hydrogen-like atom composed of an electron and a positron (rather than an electron and a proton) arising as a positron is slowed down in matter and captured by an electron. Two forms are known. Parapositronium, in which the spins of the positron and electron are oppositely directed, decays by annihilation into two photons, with a mean life of about one-tenth of a nanosecond (or 10-10 second; a nanosecond is 109 second); and orthopositronium, in which the spins are in the same direction, annihilates into three photons with a mean life of about 100 nanoseconds (10-7 second). The properties of positronium corroborate the quantum theory of electrodynamics for a two-particle system

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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