At approximately what energy does pair production begin to occur?

At approximately what energy does pair production begin to occur?

• A. 0.5 MeV
• B. 1.02 MeV
• C. 2.0 MeV
• D. 10 MeV

Answer: (B)

Pair production needs enough energy to create a real electron-positron pair. Each has a rest energy of 0.511 MeV, so creating both requires at least 0.511 + 0.511 = 1.022 MeV of energy. In practice, momentum conservation with a nearby nucleus means the threshold is slightly higher, but it’s commonly quoted as about 1.02 MeV. So pair production begins at roughly 1.02 MeV. Energies well below this can’t produce the pair, while energies above it can, with increasing likelihood as energy grows.

Pair production needs enough energy to create a real electron-positron pair. Each has a rest energy of 0.511 MeV, so creating both requires at least 0.511 + 0.511 = 1.022 MeV of energy. In practice, momentum conservation with a nearby nucleus means the threshold is slightly higher, but it’s commonly quoted as about 1.02 MeV. So pair production begins at roughly 1.02 MeV. Energies well below this can’t produce the pair, while energies above it can, with increasing likelihood as energy grows.