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What is spontaneous fission and why does it occur?
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nuclear fission
Italian-born physicist Enrico Fermi explaining a problem in physics, c. 1950. He was awarded the 1938 Nobel Prize for Physics.
Spontaneous fission is a form of radioactive decay where an unstable nucleus of a heavy element splits into two nearly equal, lighter fragments without any external influence, such as neutron bombardment.123
Why It Occurs
This process is governed by the laws of quantum mechanics. Even when a nucleus is in its ground state and confined within a fission barrier, there is a small, finite probability that it will transition into an energetically favored configuration of two fission fragments. This occurs through quantum tunneling, where the system penetrates the energy barrier.2
Key Characteristics
- Occurrence: It is observed in nuclides with a mass number of 230 or greater.1
- Competition: It often competes with alpha decay. For uranium-238, alpha decay is significantly more probable, whereas for heavier artificial elements like fermium-256, spontaneous fission becomes the dominant decay mode.13
- Energy: The process releases a large amount of energy, typically 150 to 200 MeV, as the fragments are pushed apart by electrical repulsion.13
It is distinct from induced fission, which powers nuclear reactors.13