Map of nuclear binding energy
This map of the nuclei is coloured according to the average binding energies of its protons and neutrons - in other words, the amount of energy needed to separate the nucleus into its constituent nucleons divided by the number of these nucleons. The higher the binding energy, the more stable the nucleus. The most stable nuclei lie at the bottom of the black 'well' shown above, iron- 56. Uranium 235, with its 133 neutrons and 92 protons, is located in the orange zone the furthest away from the well of stability. The two fragments formed by the fission of uranium each contain around 40 or 50 nucleons and are therefore in the more stable blue and green zones. As uranium splits, each of the 235 nucleons gains stability, each releasing 0.8 MeV of energy in the process. These 0.8 MeV combine to form the 200 MeV of kinetic energy carried away by the fission products.