PhysicsChapter 7: Quantum Physics
Pair Production
Pair production
Definition
Pair production is a process in which a sufficiently energetic photon is converted into a particle-antiparticle pair, commonly an electron and a positron, in the presence of another body such as a nucleus to conserve momentum.
Why a Nearby Nucleus?
An electron has rest energy: m_ec² A positron has the same rest mass. Therefore minimum total rest energy required is: 2m_ec² For electron-positron production: approximately: 2mec² = 1.022 MeV Thus photon energy must satisfy: Eγ ≥ 1.022 MeV in the usual nuclear-field process, with any energy above the threshold contributing to kinetic energy and recoil. A photon cannot generally convert to an electron-positron pair in empty space while simultaneously conserving both energy and momentum. A nearby nucleus can take recoil momentum.
Charges
Electron: **−e Positron: +e**
Formula / Key Relation
**Eγ ≥ 2m_ec² Electron-positron rest-energy threshold: ≈1.022 MeV**
Exam preparation
Exam Focus
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Review the key facts, formulas and checks before you move on.Pair Production
Sticky Notes · Quick Revision
Pair production:
- Photon energy
- → electron `−e`
- positron `+e`
- Minimum rest energy:
- `1.022MeV`
60-second revision
- High-energy photons can produce matter-antimatter pairs.
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