The atomic bomb -also called the A-Bomb- is a destructive weapon, marked by its great explosive power. It works on the principle of nuclear fission, in which uranium-235 or plutonium-239 is used to undergo fission. When a neutron strikes the nucleus of an atom of uranium-235 or plutonium-239, the nucleus fissions or splits.During such process, a great deal of gamma rays and thermal energy are produced, in addition to two or more neutrons that set out to split the surrounding nuclei, forming what is referred to as a chain reaction. The amount of energy produced during fission is relative to the material involved. It is estimated that one kg of uranium-235 -when completely fissioned- releases amounts of energy that are equivalently produced by 17,000 tons of TNT. The thermal energy released in an A-Bomb explosion may reach temperatures of several million degrees, forming a huge fire ball great enough to ignite ground fires that can destroy an entire small city.