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 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 511Kev and moving in 2 opposite directions.
- e− + e+ ------> γ + γ
Where e− is the electron , e+ is the positron and γ is gamma rays emitted.
511Kev is the approx. 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 special importance as it is the basis of positron emission tomography.
- 1. MEDICAL IMAGING PHYSICS Fourth Edition (Wiley)