Students should be able to compare the hazards associated with…

The idea

Contamination means radioactive material gets onto or into an object or person, so the source travels with them and keeps exposing them until removed or decayed. Irradiation means exposure to radiation from a source outside the body; the person does not become radioactive and exposure stops when they move away or the source is shielded. Compare hazards by asking whether the source is internal or external, how long exposure lasts, and which radiation is most dangerous. For example, an alpha emitter is a serious contamination hazard if inhaled or swallowed because alpha particles deposit intense energy in internal living tissue. However, the same alpha source outside the body is a minor irradiation hazard because it is stopped by dead skin.

What earns the marks

• Defines contamination as radioactive material being transferred onto or into an object or person, making that object or person a continuing source of radiation.
• Defines irradiation as exposure to radiation from a source that remains outside the body, so the exposed person does not become radioactive.
• Compares duration of hazard: contamination persists until the material is removed or decays, whereas irradiation lasts only while the person remains near the source.
• Compares hazard by radiation type: alpha emitters are especially hazardous inside the body through contamination, while beta and gamma emitters are more penetrating and so more hazardous as external irradiation.
• Explains that protective measures differ: containment and hygiene reduce contamination, while distance, shielding and limited exposure time reduce irradiation.
• Uses a correct example, such as an inhaled alpha source compared with standing near a sealed gamma source, to support the comparison.

Common mistakes and how to put them right

• Saying a person who has been irradiated becomes radioactive.

  Put it right: Irradiation leaves no radioactive material on or in the person, so they are not a source afterwards.

• Treating contamination and irradiation as the same hazard.

  Put it right: Contamination involves radioactive material being where it should not be, while irradiation is exposure to radiation from a source elsewhere.

• Claiming alpha emitters on intact skin are highly dangerous.

  Put it right: Alpha radiation is weakly penetrating and stopped by dead skin, so it is most hazardous when inhaled or swallowed (internal contamination).

Exam tips

• Structure the comparison around two clear questions: is the source inside or outside the body, and how long does the exposure last?
• Name the radiation type and link it to penetration and ionising power when judging which hazard is greater.
• Use a short concrete example in each comparison, such as an inhaled alpha source versus a sealed gamma source, to show understanding rather than repeating definitions.