# Pair production

hi,

i just need a quick clarification on pair production.

from my limited understanding, a photon of sufficiently high energy (gramma ray with energy at least equal to the mass of both an electron and positron at rest) will interact with a nucleus in ways that i do not understand to produce a particle pair - an electron and a positron.

i thought, though, that when a particle and its antiparticle meet, they annihilate. would this be the case in this scenario? or would the vectors of the produced particles be such that they would never meet?
if they do annihilate, would the energy produced be equal to the energy of the initial gamma ray? if not, where in the process is energy lost?
if it is the case that annihilation occurs without energy loss, could this scenario repeat ad infinitum?

(in addition, if someone could explain the interaction between the gramma ray photon and the nucleus without resorting to complex maths, i would be much obliged)

thanks!

mfb
Mentor
i thought, though, that when a particle and its antiparticle meet, they annihilate. would this be the case in this scenario?
They do not have to annihilate, and pair production is not exactly, but similar to the opposite direction.
or would the vectors of the produced particles be such that they would never meet?
Usually, yes.
if they do annihilate, would the energy produced be equal to the energy of the initial gamma ray? if not, where in the process is energy lost?
A tiny part of the energy will go to the nucleus.
if it is the case that annihilation occurs without energy loss, could this scenario repeat ad infinitum?
No. Apart from the energy lost to the nucleus, annihilation will produce (at least) two photons, both with (roughly) half the energy of the initial photon. In addition, it is rare that the produced particle pair annihilates again.
in ways that i do not understand
Quantum field theory. It just happens.

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