Fission that occurs spontaneously, not induced by an incident particle. A type of radioactive decay. Related to fission. Related to fission fragment. Related to fission neutron. Related to fission product. Related to photofission. Related to ternary fission.
Spontaneous fission (SF) is a form of radioactive decay characteristic of very heavy isotopes, and is theoretically possible for any atomic nucleus whose mass is greater than or equal to 100 amu (elements near ruthenium). In practice, however, spontaneous fission is only energetically feasible for atomic masses above 230 amu (elements near thorium). The elements most susceptible to spontaneous fission are the high-atomic-number actinide elements, such as mendelevium and lawrencium, and the trans-actinide elements, such as rutherfordium.