Well PAIR PRODUCTION means that,When photons of a considerable energy collide with an atom's nucleus, it leads to formation of a matter particle means electron and an anti matter particle means positron.----the energy released is ample enough to ionise the positron and electron..hence they move ahead in the material...although it is for a short while.
Every known particle has an antiparticle; if they encounter one another, they will annihilate with the production of two gamma-rays. The quantum energies of the gamma rays is equal to the sum of the mass energies of the two particles (including their kinetic energies). It is also possible for a photon to give up its quantum energy to the formation of a particle-antiparticle pair in its interaction with matter.
The rest mass energy of an electron is 0.511 MeV, so the threshold for electron-positron pair production is 1.02 MeV. For x-ray and gamma-ray energies well above 1 MeV, this pair production becomes one of the most important kinds of interactions with matter. At even higher energies, many types of particle-antiparticle pairs are produced.
Electron-Positron Pair Production
When a photon has quantum energy higher than the rest mass energy of an electron plus a positron, one of the ways that such a photon interacts with matter is by producing and electron-positron pair.
|The rest mass energy of the electron is 0.511 MeV, so for photon energy above 1.022MeV, pair production is possible. For photon energies far above this threshold, pair production becomes the dominant mode for the interaction of x-rays and gamma-rays with matter.|