In positronium, the electron and positron effectively orbit around each (like the stars in a binary star system). Positronium is unstable, the electron and positron annihilate forming two photons each with an energy of 511 keV (the rest mass of the electron).
In ortho positronium, which has a mean life of 1.39 × 10-7 s, the spins of the positron and electron are parallel, in a triplet state. In para positronium, which has a mean life of 1.25 × 10-10 s, the spins are antiparallel, in a singlet state.
Related category PARTICLE PHYSICS
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