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. The irradiation will stop as soon as the source is removed.

If we are irradiated by radioactive decay, it can damage our cells and potentially kill them. 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, irradiation can be used to sterilise surgical instruments or destroy cancer cells in patients’ bodies.


Contamination refers to the unwanted presence of radioactive material on surfaces, in liquids or within the human body. A substance is radioactive if it contains radioactive particles that emit radiation.

  • A material does not become radioactive just by being irradiated; it only becomes radioactive if it is contaminated.

If someone is holding a safely contained radioactive source, they aren’t necessarily contaminated. However, if radioactive material unintentionally transfers to them, they are contaminated and could pose a radiation risk to others.

The severity of the risk depends on the nature and amount of the radioactive material.

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 distanceContamination can be prevented by using airtight clothing. However, once an object is contaminated, it can be very difficult to decontaminate it completely.

Minimising irradiation and avoiding contamination

There are risks involved when dealing with radioactive materials, the potential harm depends on the nature and 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:

  • Wear protective clothing, such as gloves and lead aprons, to avoid contact with bare skin and the clothes underneath.
  • Use 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.