Uranium-235
Uranium-235 is an isotope of uranium that differs from the element's other common isotope, uranium-238, by its ability to cause a rapidly expanding chain fission reaction. It absorbs a thermal neutron and splits into two lighter substances by way of thermonuclear fission. It either releases 2 or 3 neutrons and continues the reaction. In nuclear reactors, the reaction is slowed down by the addition of control rods which are made of elements such as boron, cadmium, and hafnium which can absorb a large number of neutrons without decaying. In nuclear bombs, the reaction is uncontrolled and the large amount of energy released creates an explosion.
