Subject knowledge and
challenging concepts
- In order to understand both fission and fusion, students need to have an understanding of atomic structure.
- Fission is when the nucleus of an atom splits (fissures) into parts. This may happen because the nucleus is unstable or it may happen because the nucleus has been struck by a sub-atomic particle. Uranium 238 and Plutonium 239, for example, are both capable of spontaneous fission but fission can be induced if they are hit by neutrons. The resulting particles may subsequently strike other nuclei, causing them to fissure. This is a chain reaction. If it is uncontrolled, it may cause other fissures to take place at an increasing rate.
- Nuclear weapons cause destruction by causing uncontrolled chain reactions from induced fission; this releases large amounts of energy.
- Nuclear reactors involve the release of energy from controlled chain reactions. This control comes from moderator materials absorbing some of the subatomic particles and thus limiting the rate at which fission takes place.
- Fission results in the release of a wide range of unstable neutron-rich products with a wide range of half-lives.
- Fusion is when smaller atomic particles such as hydrogen and helium are combined to produce larger, heavier ones. The conditions for this are extremely high temperature (millions of �C) and pressure. Energy is released. Nuclear fusion takes place in the Sun and other stars and it is the release of energy that causes, amongst other things, the emission of light.
- Producing the necessary conditions for fusion has been extremely difficult on Earth. However, one of the reactants, deuterium, has been found in the oceans in large quantities. The reaction this is used for is:
21H + 31H = 42He + 10n