Noun
positronium (plural positroniums or positronia) (Symbol: Ps)
(physics, chemistry) An exotic atom (specifically, an onium) consisting of a positron (anti-electron) and an electron, as a particle–anti-particle bound pair with no nucleus.
So finally, the energy levels of positronium are given by :: The lowest energy level of positronium ( ) is 6.8 electronvolts (eV). Source: Internet
If the electron and positron have negligible momentum, a positronium atom can form before annihilation results in two or three gamma ray photons totalling 1.022 MeV. Source: Internet
This is a bound quantum state known as positronium. Source: Internet