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A short-lived association of an electron and a positron bound together in a configuration resembling the hydrogen atom.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Atomic Physics) physics a short-lived entity consisting of a positron and an electron bound together. It decays by annihilation to produce two or three photons
[C20: from positron + -ium]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˌpɒz ɪˈtroʊ ni əm)

a short-lived atomic system consisting of a positron and an electron bound together.
[1945; positron + -ium2]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
References in periodicals archive ?
The positron preferentially forms and annihilates from a bound state called positronium (Ps).
Gidley, "Depth-profiled positronium annihilation lifetime spectroscopy on porous films," Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol.
The increased sensitivity of J-PET with respect to previous discrete symmetry tests with o-Ps[right arrow]3[gamma] is achieved by a large geometrical acceptance and angular resolution of the detector as well as by improved control of the positronium atoms polarization.
Under given circumstances, both particle and antiparticle can form a bound state, called positronium (Ps) [23].
We attempt to validate our theory by exploring the hydrogenoid atomic model with mass-ratio varying by three orders of magnitude to include the hydrogen, muonium and positronium atoms.
Among his topics are the diffraction of particles in polarized crystals, positronium and muonium spin rotation and oscillations, the phenomenon of time-reversal violating magnetic field generation by a static electric field and electric field generation by a static magnetic field, spin rotation of particles moving in bent crystals and measuring the magnetic moment of short-lived particles and nuclei, and synchrotron-type radiation processes in crystals and polarization phenomena accompanying them.
Pethrick, "Positronium annihilation studies of polycarbonate, polyethersulphone and polysulphone," European Polymer Journal, vol.
This is done to eliminate the possibility of the trapping of positrons and quenching of positronium (the metastable bound state of the positron and an electron) by the air and gases otherwise getting trapped within the powdered sample [13].
Dauwe, "Positronium trapping in free volume of polymers," Radiation Physics and Chemistry, vol.
In the lab, the researchers took the first step towards measuring the free fall of "positronium" - a bound state between a positron and an electron.
He and Allen Mills did the first laser spectroscopy of positronium, the bound state of an electron and positron in 1982.