Fission of the uranium-235 (or plutonium-239) nuclei can be induced by bombarding the nucleus with neutrons. Neutrons are released with the daughter nuclei and these neutrons are capable of causing further fissions if they collide with other uranium-235 nuclei. This results in a chain reaction and a huge amount of energy is released in a short time.Fission occurs because the binding energy of the products is more than the binding energy of the original nucleus and so the products are more stable. The fragments repel each other with enough force to overcome the strong nuclear force. The difference in binding energies is the energy released. Many different fission products are possible.