Irradiation and contamination

Shining visible radiation from a torch beam onto a hand lights the hand up because the hand has been exposed to light.


Exposing objects to beams of radiation is called irradiation. The term applies to all types of radiation including radiation from the nuclei of atoms.

Irradiation from radioactive decay can damage living cells. This can be put to good use as well as being a hazard.

Irradiation for sterilisation

Irradiation can be used to preserve fruit sold in supermarkets by exposing the fruit to a radioactive source - typically cobalt-60. The gamma rays emitted by the cobalt will destroy any bacteria on the fruit but will not change the fruit in any significant way. The process of irradiation does not cause the irradiated object to become radioactive.


Contamination occurs if an object has a radioactive material introduced into it. An apple exposed to the radiation from cobalt-60 is irradiated but an apple with cobalt-60 injected into it is contaminated.

As with irradiation, contamination can be very useful as well as being potentially harmful.

Irradiation versus contamination

The two processes of irradiation and contamination are often confused. However they are very different and useful in their own right.

Irradiation Contamination
Occurs when an object is exposed to a source of radiation outside the object Occurs if the radioactive source is on or in the object
Doesn’t cause the object to become radioactive A contaminated object will be radioactive for as long as the source is on or in it
Can be blocked with suitable shielding Once an object is contaminated, the radiation cannot be blocked
Stops as soon as the source is removedIt can be very difficult to remove all of the contamination