Suppose 3 neutrons are released by an atom of U-235 in the first stage of a fission chain reaction. Each of these neutrons has enough energy to cause another fission reaction in another nucleus of U-235, releasing more neutrons. And if all of those 2nd stage neutrons cause other nuclei to fission in a 3rd stage, how many total U-235 atoms will have undergone fission after these 3 stages of the chain reaction?
