Contamination and irradiation


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.

Radioactive beams can be used to preserve fruit 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 alter the fruit in any significant way.

Irradiation does not cause radioactivity.

The method can also be used to sterilise surgical instruments.


Contamination occurs if an object has a radioactive material introduced into (or onto) 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.

Doctors can deliberately contaminate a patient's body when it will help with diagnosis with a radioactive source, such as:

  • drinking a radioactive mixture (barium meal) will make soft tissue such as your intestine show up on an x-ray
  • technetium-99 is a radioactive isotope that can be introduced into the body to make soft tissue such as the brain or the thyroid show up on a scanner

Irradiation versus contamination

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

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 or moving away.Once an object is contaminated, the radiation cannot be blocked from it.
Stops as soon as the source is removed.It can be very difficult to remove all of the contamination.