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High energy (~GeV) positrons are seen within cosmic rays and observation of anarrow line at 511 keV shows that positrons are annihilating in the galaxyafter slowing down to ~keV energies or less. Our state of knowledge of theorigin of these positrons, of the formation of positronium 'atoms', and of thecircumstances of their annihilation or escape from the galaxy are reviewed andthe question of whether the two phenomena are linked is discussed.

Positrons in the Galaxy: their births, marriages and deaths