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