If atomic mass differences are taken into consideration, it seems that almost any element above iron is capable of spontaneous fission. The fact that these elements are not observed to decay by spontaneous fission must be due to the extremely small probability of spontaneous fission in elements below uranium. The probability of fission is proportional to the fission parameter, Z2/A. Only if the element is actually observed to decay by spontaneous fission is the chart of possible fission fragments calculated. The calculation is performed for the emission of between zero and four neutrons. The more neutrons produced, the less energy liberated by fission.

The five graphs are charts showing the energy liberated by the various combinations of the two decay fragments. The charts are necessarily symmetrical. It seems that for the very heaviest nuclides, the most energy is liberated by splitting into two fairly equal fragments, as in Hassium-264, shown above; notice here the two stalactite-like spikes at Iron-56 and Lead-208. For lighter nuclides, there is a slight bias towards 47%:53% splitting as is evident in Plutonium-242. For yet lighter nuclides, there are positively forbidden splittings covering a wide ±5% band centred on 25%:75% unless more than three neutrons are also emitted, as in Curium-246. Notice that there is a much smaller, but not insignificant, liberated energy for light:heavy splittings, this includes alpha decay, but others involving Carbon-12 or Oxygen-16 emission may be more likely.