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

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

Contamination to check for leaks

Water supplies can be contaminated with a gamma-emitting radioactive isotope to find leaks in pipes. Where there is a leak, contaminated water seeps into the ground, causing a build-up of gamma emissions in that area. The build-up of gamma emissions can be found using a Geiger-Muller tube; this makes it easier to decide where to dig to find the leak.

Gamma rays concentrated at the pipe leak, underneath the a normal residential road.

The isotope used for this purpose must:

  • be a gamma emitter
  • have a half-life of at least several days to allow the emissions to build up in the soil
  • not be poisonous to humans as it will form part of the water supply
Advantages of contaminationDisadvantages of contamination
Radioactive isotopes can be used as medical and industrial tracersRadioactive isotopes may not go where they are wanted
Use of isotopes with a short half-life means exposure can be limitedIt can be difficult to ensure that the contamination is fully removed so small amounts of radioisotope may still be left behind

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 objectOccurs 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 shieldingOnce an object is contaminated, the radiation cannot be blocked
Stops as soon as the source is removed It can be very difficult to remove all of the contamination
Move on to Test