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Which isotopes are fissile and can be split by slow neutrons?
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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.
In nuclear physics, fissile materials are defined as isotopes capable of undergoing nuclear fission when struck by slow (low-energy) neutrons, such as thermal neutrons. While many heavy nuclei can fission when excited, only a specific few do so readily and consistently with slow neutrons.12
The primary fissile isotopes utilized in the nuclear industry are:
- Uranium-235: The only fissile isotope that occurs naturally in significant amounts, though it makes up only about 0.7 percent of natural uranium.312
- Uranium-233: An artificially produced isotope generated from thorium-232 through neutron capture.31
- Plutonium-239: An artificially produced isotope created from uranium-238 via neutron bombardment.312
- Plutonium-241: Another fissile isotope that can be generated through neutron capture in plutonium-240.1
It is important to distinguish these from fertile materials, such as uranium-238 and thorium-232, which are not fissile themselves but can be converted into fissile isotopes through neutron absorption.31