Nuclear fission
- Nuclear fission is the splitting of a large and unstable nucleus, such as uranium or plutonium, into two smaller nuclei of roughly equal size.
- Spontaneous fission is rare. Usually the nucleus must first absorb a neutron.
- Fission releases energy, two or three neutrons and gamma rays. All the fission products have kinetic energy.
Chain reactions
- The neutrons released may go on to start more fission reactions, causing a chain reaction.
- In a nuclear reactor, the chain reaction is controlled to control the energy released: control rods absorb neutrons, and a moderator slows neutrons down so they can be absorbed by fuel nuclei.
- The explosion caused by a nuclear weapon is the result of an uncontrolled chain reaction.
Nuclear fusion
- Nuclear fusion is the joining of two light nuclei to form a heavier nucleus.
- In this process, some of the mass may be converted into the energy of radiation.
- Fusion powers the stars, including the Sun, where hydrogen nuclei fuse to form helium.
Using fission and fusion
- Nuclear power stations use fission to heat water, making steam to turn turbines and generate electricity.
- Fusion would produce more energy and less radioactive waste, but it needs extremely high temperatures and pressures, so it is not yet used to generate electricity.
Key terms
- Nuclear fission
- The splitting of a large, unstable nucleus into two smaller nuclei, releasing energy.
- Nuclear fusion
- The joining of two light nuclei to form a heavier nucleus, releasing energy.
- Chain reaction
- When neutrons from one fission go on to cause further fissions.
- Control rods
- Rods that absorb neutrons to control the chain reaction in a reactor.
- Moderator
- A material that slows down neutrons so they can cause fission.
- Uranium
- A heavy element used as fuel in nuclear reactors.