Why Can't a Lower Energy Photon Remain After Pair Production?

In summary, pair production occurs when a photon with an energy greater than 1.02 MeV interacts with a nucleus, creating an electron-positron pair. However, if the photon has a lower energy, it is unlikely that a final photon with energy between 0 and 8.98 MeV will exist after the interaction. This is due to the suppression of the rate of this occurrence by the fine structure constant and phase space factor. This can be seen through the Feynman diagram, which requires an additional electromagnetic vertex and results in a 3-body final state.
  • #1
TheCanadian
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In pair production, if the photon has an energy greater than 1.02 MeV, why can't a lower energy photon remain after creation of the electron-positron pair? For example, if you have a 10 MeV photon interacting with a carbon nucleus, why are the stated products of pair production the carbon nucleus, positron, and electron? Why can't a final photon with energy between ## 0 < E_\gamma < 8.98## MeV exist afterwards from this interaction with the carbon nucleus?
 
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  • #2
In principle, there is nothing forbidding this. However, the rate of this occurring is going to be suppressed by the fine structure constant and some phase space factor.
 
  • #3
Orodruin said:
In principle, there is nothing forbidding this. However, the rate of this occurring is going to be suppressed by the fine structure constant and some phase space factor.

Do you mind providing a resource/explanation discussing this calculation and why it's unlikely by a factor of the fine structure constant/phase space difference?
 
  • #4
It should be pretty obvious at A level. The Feynman diagram needs an extra electromagnetic vertex and it is a 3-body final state.
 
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FAQ: Why Can't a Lower Energy Photon Remain After Pair Production?

What is the lower limit in pair production?

The lower limit in pair production refers to the minimum energy required for a photon to produce an electron-positron pair. This minimum energy is determined by the rest mass of the particles being produced.

How is the lower limit in pair production calculated?

The lower limit in pair production is calculated using the equation E = 2mc², where E is the minimum energy required, m is the rest mass of the particles, and c is the speed of light. This equation is derived from Einstein's famous equation, E=mc², which relates mass and energy.

Why is the lower limit in pair production important?

The lower limit in pair production is important because it determines whether or not a photon has enough energy to produce an electron-positron pair. If the photon's energy is below the lower limit, pair production cannot occur. This limit also helps us understand the behavior of particles at high energies.

What happens if a photon's energy is above the lower limit in pair production?

If a photon's energy is above the lower limit, it can produce an electron-positron pair. This process is known as pair production and is a fundamental process in particle physics. The photon's energy is converted into the mass of the particles produced.

How does the lower limit in pair production relate to the concept of mass-energy equivalence?

The lower limit in pair production is a direct result of mass-energy equivalence, which states that mass and energy are two forms of the same thing and can be converted into one another. In pair production, the energy of a photon is converted into the mass of the particles produced, following the equation E = mc².

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