In particle physics, when an electron and positron annihilate, they produce two photons that travel in opposite directions to conserve linear momentum. This process requires both energy and momentum conservation, meaning that pair production cannot occur with a single photon unless it possesses sufficient energy and interacts with a nucleus. Specifically, two photons, each with energy greater than 511 keV, are necessary for pair production, or alternatively, a single photon with energy exceeding 1022 keV can achieve this in the presence of an atom.
PREREQUISITESThis discussion is beneficial for students and professionals in physics, particularly those focusing on particle physics, as well as educators teaching concepts related to particle interactions and conservation laws.
Yes, it is true, but “I read somewhere” isn’t a good reference. You should usually explicitly state where you read it.DiracPool said:I read somewhere that when, say, an electron and positron annihilate, they create two photons which travel in opposite directions in order to conserve linear momentum. Is this true?
Both energy and momentum must be conserved (as well as charge, spin, etc). So one photon cannot do it.DiracPool said:Do you likewise need two photons to do this? Or, can you do it with one photon provided it has enough energy?