Radioactive contamination vs irradiation

Two distinct hazards from radioactivity, often confused at GCSE.

Irradiation

Irradiation is exposure to radiation from an external source. The object isn't itself radioactive — it just received radiation. When the source is removed, irradiation stops.

• Examples: an X-ray scan, gamma-sterilisation of food, sunbathing.
• Radiation can ionise tissue but the object/person doesn't become radioactive.
• Distance and shielding reduce the dose.

Contamination

Contamination is when radioactive material gets onto or into the person/object. The contaminating substance continues to emit radiation after removal of the source.

• Examples: dust from a nuclear accident landing on clothes; radioactive iodine ingested.
• Continues to expose tissue from inside until it's removed or decays.
• Hard to detect/clean once internalised.
• Contamination by an alpha-emitter is particularly dangerous because alpha is highly ionising and the body can't shield itself from a source inside.

Hazard comparison

Aspect	Irradiation	Contamination
Where source is	Outside	On or in
Stops after distance?	Yes	No (until source decays/removed)
Worst type	High-energy γ	α (or β) inside body
Shielding helps?	Yes	No (already past it)

How to limit exposure

• Time — minimise duration near a source.
• Distance — radiation intensity falls off with distance (inverse-square for a point source).
• Shielding — use lead/concrete for γ; aluminium for β; paper-thick for α.
• For contamination: hand-washing, protective clothing, sealed handling, decontamination.

Peer review and safety

Reports of radiation safety undergo peer review by independent scientists. This catches errors and fraud. Public confidence in nuclear medicine and power depends on transparent peer-reviewed evidence.