<Li> Spallation--a nucleus is hit by a particle with sufficient energy and momentum to knock out several small fragments or smash it into many fragments . </Li> <Li> Induced gamma emission belongs to a class in which only photons were involved in creating and destroying states of nuclear excitation . </Li> <Li> Alpha decay--Though driven by the same underlying forces as spontaneous fission, α decay is usually considered to be separate from the latter . The often - quoted idea that "nuclear reactions" are confined to induced processes is incorrect . "Radioactive decays" are a subgroup of "nuclear reactions" that are spontaneous rather than induced . For example, so - called "hot alpha particles" with unusually high energies may actually be produced in induced ternary fission, which is an induced nuclear reaction (contrasting with spontaneous fission). Such alphas occur from spontaneous ternary fission as well . </Li> <Li> Fission reactions--a very heavy nucleus, after absorbing additional light particles (usually neutrons), splits into two or sometimes three pieces . This is an induced nuclear reaction . Spontaneous fission, which occurs without assistance of a neutron, is usually not considered a nuclear reaction . At most, it is not an induced nuclear reaction . </Li>

Where does the energy of a nuclear reaction come from