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Nuclear Safeguards Education Portal
  

Fission

Cross-section of U-235
Cross-section of U-235 

One possible mode of decay for very heavy nuclides is via fission. If a very large nucleus has an excess of energy, it may decay by splitting into two smaller nuclei. These smaller nuclei are referred to as fission products. Fission may also result in the production of various types of radiation including gamma-rays, several neutrons, and neutrinos. These different types of radiations will be discussed in more detail later. Fission generates a large amount of energy.

U-235 Fission
U-235 Fission.

Fission can occur spontaneously (i.e., through radioactive decay) or it can be induced by bombarding a nucleus by a neutron or a highly energetic photon. In nuclear reactors, fission occurs primarily through neutron bombardment. The neutrons produced from this fission reaction can go on to cause additional fission reactions. This leads to a chain reaction which is self-propagating. Nuclear reactors rely upon chain reactions in which each fission reaction results in on average one neutron that will go on to cause an additional fission reaction.

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