This was one of the alchemists' big quests, and it is evident that it is impossible with the methods that they had available. But how feasible is it to do that with nuclear reactions? Especially nuclear reactions that start with relatively common materials, like hydrogen or carbon or silicon or iron or lead. This question can be broken down into parts. How energy-efficient are particle accelerators? Efficiency being how much energy goes into a particle divided by the wall-plug electrical energy involved in accelerating that particle. In effect, (particle flux) * (energy per particle) / (total energy consumed by the accelerator) I'd only need this for accelerators that do a few MeV per unit charge, because those are what one would need for nuclear reactions. What are the most suitable sorts of reactions? Direct acceleration of nuclei into targets? Or releasing neutrons by spallation and then using those neutrons. What branching fractions to such reactions typically have? I'm asking this here because it's hard to find the appropriate numbers, like for particle-accelerator energy efficiency. If this forum is an unsuitable place for this question, then feel free to move it elsewhere.