AQA A-Level Physics/Particles and Anti-particles/Creation and annihilation
All particles have a corresponding anti-particle, which has equal mass and opposite charge. For example the positron, the anti particle of an electron, is exactly the same as an electron but with a positive charge. A particle and its corresponding anti particle are created through pair production and destroyed through annihilation. This theory comes from Einstein's 'Special theory of Relativity' through which mass can turn into energy and energy into mass. The equation is E=MC2.
Pair production is a process which happens when a gamma ray photon splits into a particle and an antiparticle, this will only happen if the photon has enough energy to produce the mass of the two particles. This usually occurs near a nucleus, which helps to conserve the momentum of the gamma ray photon. Electron-Positron pairs are produced more often than any other pairs as they have relatively low masses.
The opposite of Pair Production is Annihilation. When a particle meets its equivalent anti particle (eg. an electron colliding with a positron) the two, having exact opposite charges are automatically destroyed. All the mass that has been destroyed in this process is changed into energy in the form of two gamma ray photons.