# Pair production

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#1
Hi everyone I was wondering is someone could give me an explanation of pair production and an example of pair production as I am struggling with the way that my teacher has explained it.
Many thanks
1
4 years ago
#2
Hi! I'm assuming you mean in particle physics? We've just covered that at school (I'm studying AQA A Level and I'm in Year 12) so I'll try my best to explain...
Occasionally, gamma rays (very high frequency electromagnetic waves) spontaneously create a particle (eg an electron) and an antiparticle (eg a positron - the antimatter counterpart of an electron, with the same mass but an opposite charge).
Gamma rays, like all electromagnetic waves, are made up of photons (little packets of energy that act like particles). In pair production, an individual photon splits up into a particle and an antiparticle.
Pair production is more likely to happen if the gamma ray has just passed a nucleus.
In order for a photon to split into a particle and antiparticle, it needs enough energy - it needs at least as much energy as the particle and antiparticle have when they aren't moving (their rest energy, which should be on your data sheet if you have one?)
A particle and its corresponding antiparticle have the same rest energy, so to work out how much energy is needed you have to multiply the rest energy of the particle by two. The units for that are usually mega electron volts (MeV), but sometimes they'll ask you to convert that into joules - one MeV = 1.6x10 to the power of 13 Joules, so times the answer in MeV by 1.6x10 to the 13.
Using this method you can work out whether the pair production is possible- if the photon has at least enough energy as is needed, it is possible, if not it is impossible.
If the photon has more energy than is needed the particle and antiparticle gain that energy as kinetic energy.

For example...
A photon spontaneously converts into an electron and a positron. The photon has 2.0x10 to the -13 joules of energy. The minimum energy needed for this pair production is 0.51 MeV (roughly the rest energy of an electron or a positron) x 2 (because two particles with this rest energy are created). This is 1.02 MeV which is 1.02x1.6x10 to the -13 Joules which is 1.64x10 to the -13 Joules (ish). The extra 0.36x10 to the -13 Joules are converted into kinetic energy which the electron and positron gain.

I think that's everything! Sorry if it's overcomplicated/unclear - and sorry it's so long! I have trouble being concise
0
#3
(Original post by donttellme)
Hi! I'm assuming you mean in particle physics? We've just covered that at school (I'm studying AQA A Level and I'm in Year 12) so I'll try my best to explain...
Occasionally, gamma rays (very high frequency electromagnetic waves) spontaneously create a particle (eg an electron) and an antiparticle (eg a positron - the antimatter counterpart of an electron, with the same mass but an opposite charge).
Gamma rays, like all electromagnetic waves, are made up of photons (little packets of energy that act like particles). In pair production, an individual photon splits up into a particle and an antiparticle.
Pair production is more likely to happen if the gamma ray has just passed a nucleus.
In order for a photon to split into a particle and antiparticle, it needs enough energy - it needs at least as much energy as the particle and antiparticle have when they aren't moving (their rest energy, which should be on your data sheet if you have one?)
A particle and its corresponding antiparticle have the same rest energy, so to work out how much energy is needed you have to multiply the rest energy of the particle by two. The units for that are usually mega electron volts (MeV), but sometimes they'll ask you to convert that into joules - one MeV = 1.6x10 to the power of 13 Joules, so times the answer in MeV by 1.6x10 to the 13.
Using this method you can work out whether the pair production is possible- if the photon has at least enough energy as is needed, it is possible, if not it is impossible.
If the photon has more energy than is needed the particle and antiparticle gain that energy as kinetic energy.

For example...
A photon spontaneously converts into an electron and a positron. The photon has 2.0x10 to the -13 joules of energy. The minimum energy needed for this pair production is 0.51 MeV (roughly the rest energy of an electron or a positron) x 2 (because two particles with this rest energy are created). This is 1.02 MeV which is 1.02x1.6x10 to the -13 Joules which is 1.64x10 to the -13 Joules (ish). The extra 0.36x10 to the -13 Joules are converted into kinetic energy which the electron and positron gain.

I think that's everything! Sorry if it's overcomplicated/unclear - and sorry it's so long! I have trouble being concise
That is brilliant thanks so much i am in year 12 doing the same thing too xx
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