Radioactive contamination is the unwanted presence of materials containing…

The idea

Contamination means radioactive atoms have got onto or into something where they are not wanted, for example dust on a bench, soil on boots or a tracer in a water pipe. The contaminating atoms decay, so the material keeps emitting radiation until the source is removed or decays away. The hazard depends on the radiation type: alpha particles are stopped by skin but are very dangerous if the source is inhaled or swallowed, beta particles penetrate a little and can damage tissue, and gamma rays pass through the body and need dense shielding. A student should distinguish contamination from irradiation, identify the contaminating isotope, and explain how its emissions and half-life affect the risk and the clean-up method.

What earns the marks

• Defines contamination as unwanted radioactive atoms on or in another material, not as exposure to a beam of radiation.
• Explains that the hazard continues because the contaminating atoms themselves decay, so the object remains a source until the material is removed or decays.
• Links the type of emission to the hazard: alpha is most damaging inside the body, beta penetrates further, gamma is most penetrating and needs dense shielding.
• Uses half-life to judge how long a spill or contaminated item remains hazardous and to choose a suitable clean-up or storage strategy.
• Applies practical controls such as gloves, containment, ventilation, monitoring with a Geiger–Müller tube and safe disposal of contaminated waste.

Common mistakes and how to put them right

• Saying an irradiated object has become radioactive.

  Put it right: Irradiation exposes an object to radiation but does not leave radioactive atoms on it, whereas contamination does.

• Treating all contamination as equally dangerous.

  Put it right: The hazard depends on the emitted radiation, its energy, whether the material can enter the body and the half-life of the contaminating isotope.

• Assuming alpha contamination is harmless because alpha cannot penetrate skin.

  Put it right: Alpha emitters are especially hazardous if inhaled or swallowed because the alpha particles deposit energy in living tissue.

Exam tips

• Use the phrase 'unwanted radioactive atoms on or in another material' when defining contamination, then contrast it directly with irradiation.
• When asked about hazard, name the emission type and state whether the source is outside or inside the body before discussing penetration.
• For clean-up questions, link the method to the half-life and emission type, for example sealing a long-half-life alpha source or monitoring until count rate falls to background.