11. Positronium has been studied since the 1950s to understand bound states in quantum field theory.12. The properties of positronium were predicted by Carl D . Anderson of Caltech in 1932. 13. Electrons and positrons drifting through space will encounter one another and occasionally form positronium atoms. 14. Positronium is the bound state of an electron and a positron and therefore the lightest atom.15. The decay rate of the singlet ( " para-positronium " ) 1 S 0 state yields 16. The energy of the photons from positronium should differ slightly by the binding energy of the molecule. 17. Thus, for positronium , its reduced mass only differs from the electron by a factor of 2. 18. Positronium decays through the annihilation of the electron and the positron into two or more gamma-ray photons.19. For example Positronium is quite stable ( for some nanoseconds, but that is long in this case ). 20. For insulators such as polymers or zeolites, implanted positrons interact with electrons in the material to form positronium .
