Learn about fission and chain reaction, in this clip from Uranium: Twisting the Dragon's Tail. Hear Derek explain how at the center of a uranium atom is a nuclear composed of 92 protons and 146 neutrons. The nucleus is so large that it will spit out bits of itself and release energy. In Germany, physicist Otto Hahn added one more neutron to the uranium nucleus and discovered how it "fissions" into two, releasing two or three extra neutrons. Hungarian physicist Leo Szilard realized that the stray neutrons can split other uranium atoms and called this a chain reaction.