Positronium
Positronium is a quasi-stable system consisting of a
positron and an
electron bound together into an "
exotic atom." Its set of energy levels is similar to that of the
hydrogen atom (electron and
proton). However, because of the different
reduced mass, the
frequencies associated with the spectral lines are less than half of those of the corresponding hydrogen lines. The
half-life of positronium is at most about 10
-7 seconds, its existence being terminated by electron-positron
annihilation.
