^Pair annihilation
^Pair annihilation
It is the reverse of pair production effect. Experiments reveal that when a positron passes through matter & sees an electron and the two come together under the influence of their internal electric attraction, may form an atom like configuration called positronium, where they rotate around each other about the centre of mass & ultimately come close together and annihilate (vanish) each other in a time of the order of 10-10 s & the lost mass becomes the electromagnetic energy in the form of two gamma ray photons, each moving away from the other with energy 0.511 MeV in opposite direction such that both energy & linear momentum is conserved.
