Contamination and Irradiation — Radioactivity, Uses & Dangers | IGCSE Physics

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 7% of your exam marks.

stable

Low

Stable7%

Half-life calculations and uses/dangers of radioactive sources appear in most series.

These two words are commonly mixed up in exams. They describe completely different events.

Contamination is the accidental transfer of a radioactive substance onto, or into, another object

The contaminated object now physically contains radioactive atoms, usually in tiny amounts, on the surface or inside the body
Because the radioactive atoms are part of the object, the object itself is now radioactive and will keep emitting radiation until those atoms decay away
Typical examples:
- A radiation leak at a nuclear plant deposits radioactive dust on the ground and on workers' clothes
- Inhaling radioactive radon gas in a poorly ventilated cellar, where radon atoms enter the lungs and decay there
- Eating food grown on contaminated soil, so radioactive atoms enter the body

Irradiation is the process of exposing an object to ionising radiation from an external source

The object is in the path of the radiation while the source is nearby, but no radioactive material is transferred onto or into it
As soon as the source is removed or shielded, the irradiation stops, and the object is not radioactive afterwards
Typical examples:
- A patient receiving a dental X-ray is irradiated while the X-ray machine is on, but does not become radioactive
- A worker in a hospital who walks past a shielded gamma source receives a small dose of irradiation
- Food being passed through a gamma sterilisation chamber

	Irradiation	Contamination
What happens	The object is exposed to radiation from a separate source	A radioactive substance is transferred onto or into the object
Is the object radioactive after?	No, the radiation stops as soon as the source is removed	Yes, the object emits radiation until the radioactive atoms decay
Typical cause	Deliberate (X-ray, radiotherapy, sterilisation)	Accidental (leak, spill, ingestion, inhalation)

A short half-life means a high , with many decays per second per unit mass. Most of the radiation is emitted quickly
- This makes irradiation worse: while the source is active, anyone nearby is hit with a heavy stream of radiation
- For external doses (X-ray rooms, gamma sterilisers), short-half-life sources are the bigger danger
A long half-life means a low activity but lasting for a very long time
- This makes contamination worse: a contaminated object stays radioactive for years or centuries and keeps irradiating its surroundings the whole time
- For environmental clean-up (nuclear leaks, buried waste), long-half-life isotopes are the bigger danger