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Positronium
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Electron–positron bound state.
An electron–positron bound state with half the hydrogen binding energy (6.8 eV); it annihilates into gamma rays in 0.1 ns (para) or 140 ns (ortho).
Used to study QED.
Reduced mass is mₑ/2.
In more detail
Positronium is a bound state of an electron and a positron, similar to hydrogen but with a much smaller reduced mass. It annihilates after a short lifetime, emitting gamma rays.
Real-world uses
- Positronium lifetimes are used to probe materials in positron annihilation spectroscopy.
- It is a test system for quantum electrodynamics.
- Physicists study positronium, a short-lived electron–positron pair, to test quantum electrodynamics.
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Frequently asked questions
Is positronium stable?
No. It annihilates in about a tenth of a nanosecond for the singlet state.
Why is it important?
It tests predictions of bound state QED with high precision.
How long does positronium last?
Only a fraction of a microsecond, because the electron and positron annihilate quickly.
Related topics in Atomic & Nuclear Physics
Mössbauer effect · Nuclear waste · Hydrogen-like ions · Muonic atoms · Atomic clocks · Laser cooling of atoms