AQA A-Level Physics/Particles and Anti-particles/Particle-Antiparticle interactions

A high-energy photon may, under certain circumstances, produce a particle-antiparticle pair through the process of 'pair production'. On the other hand, one particle and one antiparticle, should they come into contact with each other, annihilate to give out 2 photons (i.e. a pair of electromagnetic waves) through the process of 'annihilation'.

These two processes are the essential parts of particle physics, both following the equation for mass-energy conversion first proposed by Albert Einstein, E = mc^2.

For instance, in the annihilation process of one pair of electrons and positrons, the energy created by the pair is $E=2m_e c^2$, as all mass should be conserved by being converted into energy. In the production, the frequency required for the photon to create the pair can be calculated using E = hf = 2m_e c^2.

The most common form of pair production is electron-positron production. This is because they have a smaller mass than most other particles, and thus require less energy to create. For the sake of comparison, an electron has a rest energy of 0.510999 MeV (or 8.18 x10^-14 J), meaning that a photon needs a frequency of 2.468 x10^20 Hz to create an electron-positron pair, as opposed to the proton's rest energy of 938.257 MeV (1.50x10^-10 J) and accompanying frequency of 4.53 x10^23 Hz.