Contents
Key Stage 5
Meaning
Annihilation is the process in which matter and antimatter interact converting all their rest mass into energy resulting in two or more gamma ray photons being emitted in opposite directions.
About Annihilation
- Annihilation occurs when particles of matter and antimatter interact at extremely close range.
- Follows the principle of mass-energy equivalence (E=mc²).
- During annihilation the total rest mass, as well as the kinetic energy, of the particles before the event is equal to the total energy of the products (two gamma ray photons in a-level physics) after the event.
- In annihilation conservation of momentum is conserved due to the momentum of the gamma ray photons travelling in opposite directions.
- Results in the production of gamma rays or other particles. However, for a-level physics, you only need to consider the special case of 2 gamma ray photons being emitted.
Equation
Assuming both particles are at rest
\(2E_0 = 2hf\)
Where
\(E_0\) = Rest Mass Energy of each particle
\(hf\) = The energy of eachgamma ray photon emitted
\(h\) = Planck's Constant
\(f\) = The frequency of the emitted photon
In the special case that one of the particles is in motion
\(2E_0 + E_k = 2hf\)
Where
\(E_k\) = The kinetic energy of the particle
Examples
- Positron emission tomography (PET) scans detect gamma rays from electron-positron annihilation.
- Particle accelerators study annihilation events to understand fundamental particles.