Nuclear Fission and Fusion

When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments.

In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons which react with still more fissionable atoms.

• Chain reactions can be controlled by:
  • Neutron Moderation- slows the neutrons
  • Neutron Absorption- decreases the number of slow moving neutrons

Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei and two positrons.

Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split.