2.4 Spontaneous fission

The nuclear binding energy of the elements reaches its maximum at an atomic mass number of about 58 and the spontaneous breakdown of the nucleus into smaller nuclei and a few isolated nuclear particles becomes possible, but is limited by constrains in the formation of fission products. The probability of spontaneous fission to occur increases in some isotopes with atomic masses greater than 92 atomic mass units (amu).

Spontaneous fission occurs through the splitting of heavy atoms into two fragments and the subsequent release of neutrons and energy. The decay by fission usually leaves the newly formed nucleus in an energy excited state, and the surplus energy is emitted as gamma rays.