The process that describes the splitting of a heavy atomic nucleus is known as nuclear fission. This process occurs when a heavy nucleus, such as that of uranium or plutonium, absorbs a neutron and becomes unstable, leading it to split into two smaller nuclei along with the release of energy and more neutrons. This reaction is the basis for nuclear power generation and atomic bombs, as the released energy can be harnessed for energy production or cause further fission in a chain reaction.