Irradiation and contamination


When an object is exposed to radiation, this is known as irradiation. This applies to all types of radiation, including both ionising radiation and non-ionising radiation. So, if radiation reaches the object we say it has been irradiated.

An irradiated object does not become radioactive, even if it has been exposed to radiation for a long period of time. It will stop as soon as the source is removed.

If radioactive decay irradiates us, it can damage our cells and therefore kill them off. So, the amount of irradiation that the human body is exposed to must be limited. Irradiation can be minimised by using protective measures, such as appropriate shielding and distance.

Although irradiation is harmful, it can also be useful. For example, it can be used to sterilise surgical instruments or destroy cancer cells in patients’ bodies.


Contamination occurs when radioactive substances get onto an object. A substance is radioactive if it contains radioactive particles that emit radiation.

  • A material can only become radioactive if it is contaminated.

If a person is carrying a radioactive source, they are contaminated. This means that they can cause harm to other people, giving them radiation sickness.

Radioactive source is outside the objectRadioactive source is on or inside the object
The object does not become radioactiveContaminated object will remain radioactive for as long as the radioactive source is on or inside it
Can be prevented by using suitable shielding or keeping a distanceCan be prevented by using airtight clothing. Once the object is contaminated, it can be very difficult to remove all of it.

Minimising irradiation and avoiding contamination

There are risks involved when dealing with radioactive materials, the potential harm depends on the amount of exposure.

To minimise irradiation and avoid contamination, we must take certain precautions to reduce the risk of exposure to radioactive sources.

For example:

  • Wearing protective clothing, such as gloves and lead aprons, to avoid contact with bare skin and clothes underneath.
  • Using tools, such as tongs to handle radioactive materials.
  • Wear face masks to avoid inhaling radioactive materials.
  • Limit the time spent near radioactive materials

The hazard symbol below is placed on containers that carry radioactive substances.