4PH1
Radioactivity, Uses & Dangers
Radioactivity & Particles · 1 question type
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
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
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
Side-by-side comparison
| 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) |
| Type of radiation that matters most | Penetrating types (gamma, X-ray), because they reach you from outside | Ionising types (alpha), because once inside they damage cells most |
| How to prevent | Shielding (lead, concrete), distance, short exposure time | Sealing the source, gloves, airtight suits, no eating or drinking near sources |
| Easier to deal with? | Easier; remove the source and the problem stops | Harder; must remove or wait out every contaminated atom |
Half-life and which is more dangerous
- 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