When neutrons strike the nucleus at the center of an atom, the nucleus undergoes fission and releases fission energy, at the same time releasing two or three neutrons. The newly released neutrons strike other nuclei, splitting them in the same way, causing a sequence of fissions so as to continuously produce energy. This is called a “nuclear chain reaction.” Although materials such as uranium and plutonium can undergo nuclear fission, they will not reach a state of criticality, at which the chain reaction will continue, if the material is not of a specific amount. This amount is called the “critical mass.” If the material has critical mass and fission accelerates, tremendous quantities of strong energy will be produced. This energy is of high temperature, and generates dangerous radiation. The atomic bomb (A-bomb) is a weapon of destruction that uses the power released by the splitting of atomic nuclei.