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Pair production
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Pair production results in the conversion of a gamma-ray photon into an electron-positron pair within the Coulomb field of the nucleus. The interaction is with the atom as a whole.

The process of pair production is only possible if the incident gamma-ray photon energy exceeds twice the combined rest mass energy of the electron and positron pair (1022 keV).

Ee + EpEg - 1022 keV

The ejected positron will inevitably meet a free electron and annihilate, releasing two 511 keV gamma-rays.

Have a go Use the simulation opposite to investigate pair production.

The energy absorbed by during the process of pair production can be observed as the pair production peak in the detected energy spectrum. One example of a radionuclide that produces a 511 keV photon is 22Na.


Simulation of Pair Production

 

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1999, 2000 The University of Liverpool, Department of Physics

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