Electron-positron annihilation is the process in which a positron collides with an electron resulting in the annihilation of both particles. Electrons (or β- particles) and positrons (or β+ particles) are of equal mass but opposite charge. Positrons are the antimatter equivalent of an electron, produced from B+ decay
According to the law of conservation of energy, their masses are converted to 2 annihilation gamma ray photons with an energy of around 511 keV and moving in 2 opposite directions.
e− + e+ ------> γ + γ
Where e− is the electron, e+ is the positron and γ are gamma rays emitted.
511 keV is the approximate amount of energy created when an electron or positron (which each have a mass of 9.11x10-31 kg) are converted to energy according to Einstein's famous equation:
E = mc2
Where E = energy , m = particle mass and c = velocity of light.
i.e. E= 9.11x10-31 kg x (3x108 m s-1)2.
Therefore E= 8.20x10-14 J = 511 keV.
This process is of particular importance as it is the basis of positron emission tomography.
- 1. MEDICAL IMAGING PHYSICS Fourth Edition (Wiley)