PhysicsChapter 7: Quantum Physics
Pair Annihilation
Pair annihilation
Definition
Pair annihilation is the process in which a particle and its antiparticle interact and convert their mass-energy into other particles, commonly photons.
Conservation
For an electron and positron at rest or nearly at rest: e⁻ + e⁺ → 2γ Two photons are produced in the simplest case. If the electron and positron annihilate approximately at rest: each photon has energy: Eγ≈mec²≈0.511MeV and the two photons travel in opposite directions to conserve momentum. Total photon energy: ≈1.022MeV ignoring initial kinetic energy. The process obeys: energy conservation; momentum conservation; * electric charge conservation. Pair annihilation is essentially the reverse idea of pair production.
Formula / Key Relation
**e⁻+e⁺→2γ At rest: Eγ≈0.511MeV each**
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Review the key facts, formulas and checks before you move on.Pair Annihilation
Sticky Notes · Quick Revision
Annihilation:
- `e⁻ + e⁺ → 2γ`
- Each ≈ 0
- if pair initially at rest.
60-second revision
- Annihilation demonstrates conversion of rest mass into radiation.
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