Radioactive contamination is the unwanted presence of materials containing…

The idea

Contamination means the radioactive material itself has ended up somewhere it should not be: on a bench, on skin, on clothing, or inside a body after being swallowed or breathed in. The atoms are transferred, not just the radiation they give out. That is the whole distinction from irradiation, where the source stays where it is and only the radiation reaches the object. A contaminated object carries a source that keeps decaying wherever it goes, so moving away from the original source does not help. It is why a teacher wearing polythene gloves to handle a radioactive sample is protected from contamination, even though the gloves do nothing to stop the hands being irradiated by the radiation passing through them.

What earns the marks

• Contamination being the unwanted presence of materials containing radioactive atoms on other materials.
• The radioactive material itself being transferred, on or inside a person or object.
• The contrast with irradiation, which is exposure to radiation from a source outside the object.
• A precaution such as gloves, which prevents transfer of material even though it does not stop irradiation.

Common mistakes and how to put them right

• Defining contamination as being hit by radiation, which is irradiation.

• Saying gloves stop the hands being irradiated.

• Claiming an object becomes contaminated simply by being near a source.

• Writing that 'radiation gets on you' rather than radioactive material.

• Assuming contamination is only external, when swallowed or inhaled material is the more serious case.

Exam tips

• Use the word 'material' or 'atoms' in the definition; an answer that only says 'radiation' will be read as irradiation and lose the mark.
• Examiners allow 'an object' in place of 'a person', so a general answer is safe here.
• If the question mentions gloves or clothing, the answer is almost certainly about preventing transfer of material.