Given a large enough energy source (nuclear?)... can I build a rocket that creates its own reaction mass via electron-positron pair production, and then derive thrust by accelerating the charged particles out the back with a magnetic nozzle?
Although a nuclear reaction might produce some such photons, it also produces lots of heat that just serves to melt the spacecraft. You not only need an energy source, you need a system which produces only high energy photons near nuclei, and does not do much else. You also need a way to get the electrons and positrons to the nozzle without much interaction with anything else.https://en.wikipedia.org/wiki/Pair_production said:The photon must have higher energy than the sum of the rest mass energies of an electron and positron (2 × 0.511 MeV = 1.022 MeV) for the production to occur. The photon must be near a nucleus in order to satisfy conservation of momentum, as an electron-positron pair producing in free space cannot both satisfy conservation of energy and momentum. Because of this, when pair production occurs, the atomic nucleus receives some recoil.