When the nucleus of an atom is unstable, it occasionally emits either waves or particles to stabilise itself.

The three types of radiation are: Alpha particles, Beta particles and Gamma waves.

Alpha particles are relatively large, being made up from two protons and two neutrons. These particles cannot travel far without colliding with other atoms (i.e. atoms in the air) and losing their energy. This means alpha radiation is easily stopped by even thin materials such as paper.

Beta particles are simply high energy electrons which can are much smaller than alpha particles, hence can travel further before losing their energy in collisions. A thin sheet of aluminium is capable of stopping beta radiation.

Gamma waves are high energy electromagnetic waves. It can be thought of as extremely high energy light, which is invisible to our eyes as its frequency is too high for our eyes to detect. As gamma radiation is a wave, it is not stopped as easily by collisions with atoms. This means gamma rays easily pass through human skin, its high energy can result in cancerous mutations of cells. Dense materials such as lead are required to stop gamma radiation.

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