Electron-positron annihilation

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.

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Article information

rID: 16448
Section: Physics
Tag: refs
Synonyms or Alternate Spellings:
  • Positron-electron annihilation

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Cases and figures

  • Diagram : electron-positron annihilation
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