Annihilation

Annihilation occurs when a particle and its corresponding antiparticle meet. Their mass is converted into photons of energy.

E₀ = m c²

E₀ = rest energy and m = massTwo photons are produced to conserve momentum.The minimum energy of each photon is given by

h f_min = E₀

E₀ is the rest energy of the particle.
Annihilation is used in positron emission tomography PET hospital scanners.The positron emitting isotope is administered to the patient.When it reaches the brain via the blood circulatory system it travels a few millimetres then meets an electron and they annihilate each other.Two gamma photons are sensed by detectors linked to computers and an image is built up from the detector signals.