Electron-positron annihilation is the process in which a positron (from B+ decay) collides with an electron resulting in their annihilation. Being of opposite charges and same mass they act as a collision of subatomic particle and anti-particle.
According to the law of conservation of energy, their masses are converted to 2 annihilation photons of energy (gamma rays) each of energy about 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 equivalent for the electron mass according to Einstein's famous equation:
E = mc2
Where E = energy , m = particle mass and c = velocity of light.
This process is of particular importance as it is the basis of positron emission tomography.
- 1. MEDICAL IMAGING PHYSICS Fourth Edition (Wiley)