Question on photon-nucleus pair production

In summary, a nucleus is needed for a gamma ray to interact with in particle pair production because the process requires both total energy and total momentum to be conserved. The photon, being a neutral and massless particle, creates two charged and massive particles (an electron and positron) in order for the energy and momentum to be conserved. The nucleus also helps in the conservation of momentum by providing a target for the particles to interact with. Additionally, the energy-momentum four vector for the gamma ray is a null vector, meaning it has zero magnitude, and this can only be achieved by combining the momenta of two time-like massive particles.
  • #1
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I'm having a bit of trouble understanding why a nucleus is needed for a gamma ray to interact with in particle pair production. I know that all properties are conserved - spin, charge, etc. -, and I know that the photon must have at least the energy of twice the standing energy of the particle it creates (for electron-positron pairs this is 1.022 MeV, correct?), but why does a nuetral, massles particle (photon) create two charged, massive particles (i.e. an electron and positron), and why is a nucleus necessary?
I'm asking simply out of curiosity, and any answers would be highly appreciated.
Thanks!
 
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  • #2
Try getting both total energy and total (vector) momentum before and after to add up. Remember that the energy-momentum four vector for the gamma ray is a null vector. Can you make a null vector from two time like massive particles' momenta?
 

1. What is photon-nucleus pair production?

Photon-nucleus pair production is a process in which a high-energy photon interacts with a nucleus, resulting in the creation of an electron-positron pair.

2. How does photon-nucleus pair production occur?

Photon-nucleus pair production occurs when a high-energy photon enters the electric field of a nucleus, causing it to interact with the nucleus and convert its energy into mass, resulting in the creation of an electron and a positron.

3. What is the significance of photon-nucleus pair production?

Photon-nucleus pair production is a fundamental process in particle physics and plays a crucial role in understanding the behavior of high-energy particles and the structure of nuclei.

4. Can photon-nucleus pair production occur in a vacuum?

Yes, photon-nucleus pair production can occur in a vacuum as long as the photon has enough energy to create an electron-positron pair in the electric field of the nucleus.

5. How is photon-nucleus pair production related to pair annihilation?

Photon-nucleus pair production and pair annihilation are inverse processes. In pair annihilation, an electron-positron pair collides and annihilates, resulting in the creation of a high-energy photon. In photon-nucleus pair production, a high-energy photon is converted into an electron-positron pair in the presence of a nucleus.

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