What is Fission?

    Published: 06-16-2009
    Views: 10,934
    Science expert Emerald Robinson explains what fission is.

    Emerald Robinson: Hi, I'm Emerald Robinson, and in this "What Is" video, we're going to discuss nuclear fission.

    Nuclear fission is defined as a reaction in which the nucleus of an atom is split, releasing energy and radioactivity.

    Fission occurs when an atom of a heavy element, that is, one that has a large atomic mass, splits into atoms of lighter elements. The products of the reaction have less mass than the starting atom. This difference in mass is accounted for in the energy and radioactivity release.

    Let's look at an example.

    Uranium 235 is a naturally occurring radioactive element. In a typical fission reaction, Uranium 235's nucleus absorbs a neutron moving at a low speed. This neutron causes the nucleus to become reactive, or to destabilize.

    The destabilized nucleus splits, transforming into lighter elements like Krypton and Barium. Energy and radioactivity are released, as well as multiple fast-moving neutrons. These neutrons can then go on to start another reaction with more Uranium atoms. Because the reaction starts again by itself, it's called a chain reaction. An uncontrolled chain reaction releases huge amounts of energy, and is what powers atomic bombs.

    Humans have learned to harness the energy from controlled fission reactions. In nuclear power plants, the heat energy released from the uranium fission reaction just described is used to turn water into steam. This steam is used to turn turbines, which, in turn generate electricity. Engineers control the rate of fission by using graphite rods to absorb the excess neutrons produced.

    Energy produced by nuclear fission is used by humans all around the world. Unlike burning fossil fuels, fission doesn't release carbon dioxide into the air, so it doesn't contribute to global warming. However, using nuclear power generates radioactive wastes, which makes it unpopular with some people. Fission is a powerful force of nature that man has just begun to explore.