Question

Electron and phosphitron, which are at rest in the laboratory, spin into two photons with the same energy.
1. It is measured that the two protons move in opposite directions and have the same energy. Explain why this result is necessary?
2. What is the energy (in joules) and what is the momentum of each photon (in MeV / c)?
3. How often are photons?

Answer 1

The system should be an electron and positron:

1) The initial momentum is zero, then, after the annihilation, the momentum must be zero, so both photons move in the opposite direction.

The momentum of each photon is:

then: (in opposite direction)

Using this equation:

2) For conservation of energy:

that positron and electron have initial rest energy: 0.511 MeV

then:

the momentum of each photon is: