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Pair production
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A photon converts to an electron–positron pair.
A photon with energy > 2mₑc² = 1.022 MeV near a nucleus can convert to an electron–positron pair; the nucleus absorbs the extra momentum.
Demonstrates E = mc² and antimatter.
Can't happen in empty space (momentum conservation).
In more detail
Pair production occurs when a high-energy photon creates an electron and a positron near a nucleus. The photon must have at least twice the rest energy of the electron.
Real-world uses
- Pair production occurs in gamma-ray detectors and particle accelerators.
- PET scanners use positrons from pair production processes.
- Particle physicists create electron–positron pairs in accelerators by converting high-energy photons into matter.
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Frequently asked questions
What energy is needed?
At least 1.022 MeV, the rest energy of an electron-positron pair.
Why is a nucleus needed?
It absorbs the momentum so that energy and momentum are both conserved.
Does pair production need a nucleus?
Usually yes, because a nearby nucleus or electron is needed to conserve momentum during the conversion.
Related topics in Quantum Mechanics
Stopping potential · Photon momentum · Compton effect · de Broglie hypothesis · Davisson–Germer experiment · Wave–particle duality