Question

What minimum amount of electromagnetic energy is needed to produce an electron and a positron together? A positron is a particle with the same mass as an electron, but has the opposite charge.

E=?

Answer 1

he mass-energy of a positron is 0.511 MeV, so this is the minimum energy of a photon that would be required to produce it. But we don't see a lone positron created by a gamma ray. The answer is a little more complex than that, so let's look. We see both a positron and an electron produced in an event we call pair production. The minimum energy required to produce the electron-positron pair would double that required to create the positron alone, or 1.022MeV (2 x 0.511 MeV). Lev Landau covered this in his 1934 paper, in which he describes the formation of particles from two-photon interactions from the narrow cone of gamma rays that may be formed when high energy particles collide. To answer the question directly, the minimum gamma ray energy required to produce a positron is 1.022MeV. But you'll get a positron and an electron. Again, you'll recall that only half of that minimum energy is converted into a positron, the other half being used to produce an electron.