Nuclear power stations make electricity by smashing atoms apart. Atoms are locked together by huge forces, and they release massive amounts of energy when they disintegrate.
Many elements have atoms with slightly different forms, called isotopes. Some of these are very unstable (radioactive) and naturally break apart to turn into more stable forms, releasing energy. Atoms can also be forced to split apart artificially, in nuclear power stations and atomic bombs.
Although radioactive atoms are dangerous enough to kill people, they can help to save lives as well. Radioactive particles are used in smoke alarms, and they help to preserve foods by killing harmful bacteria. They are also used to treat and detect life-threatening illnesses such as cancer.
Unstable atoms break up to release three types of radioactivity - alpha, beta, and gamma. Alpha and beta radiation are made from bits of the broken atoms. Gamma rays are a type of electromagnetic radiation, similar to light but more energetic and highly dangerous.
The slowest and heaviest forms of radioactivity are called alpha particles. Each alpha particle has two protons and two neutrons (the same as the nucleus of a helium atom).
Beta particles are smaller and faster forms of radiation. In fact, they are just streams of electrons that unstable atoms shoot out at about half the speed of light.
Penetrating power: Alpha, beta, and gamma radiation can go through different amounts of matter because they have different speeds and energy. Alpha particles can’t even get through paper. Beta particles can get through skin, but not metal. Gamma rays can only be stopped by very thick lead or concrete.
Atoms release energy in two ways. When large, unstable atoms (such as uranium) split into smaller atoms, they give off heat. This process is called fission (splitting). It creates heat because the total energy in the smaller atoms is less than the energy in the original atom.
A second process is called fusion (joining), when small atoms (hydrogen isotopes) smash together, combine, and release energy. All of the world's nuclear power stations currently work by fission, but scientists hope to build fusion stations because they will be much cleaner.
How fission works
A neutron is fired into an atom of uranium, splitting it into two smaller atoms. More neutrons are released in the process, producing a chain reaction.
How fusion works
Two heavier isotopes of hydrogen (deuterium and tritium) smash together to make helium. A spare neutron is fired out and heat energy is released.
In a nuclear power station, the heat that boils steam to make electricity isn't made by burning coal or gas, but by splitting atoms inside a giant nuclear reactor and capturing their energy. The amount of power can be controlled by raising and lowering rods to speed up or slow down the nuclear reactions.