Section 1 of 5Matching Radiation to the Job
Each use of radioactivity depends on how far the radiation travels and how strongly it ionises.
Alpha
- Alpha particles are strongly ionising but stopped by paper or a few centimetres of air,
- so they suit uses where the radiation stays inside a device.
Beta
- Beta particles pass through paper but are stopped by thin aluminium, so their transmission changes with the thickness of thin sheets.
Gamma
- Gamma rays are weakly ionising and very penetrating, so they pass through thick materials and travel long distances.
Choosing a source
- The type of radiation, its penetrating power and the half-life of the source are all considered before choosing it for a task.
Section 2 of 5Everyday and Industrial Uses
Everyday and Industrial Uses
Smoke alarms
- A weak alpha source ionises air in a small chamber;
- smoke absorbs the alpha particles, the current drops and the alarm sounds.
Thickness control
- Beta radiation passes through paper or metal foil;
- if the detector reading falls, the sheet is too thick and rollers are adjusted.
Sterilising
- Gamma rays kill bacteria on medical instruments and packaged food without making the items radioactive.
Tracers in pipes
- A gamma-emitting tracer added to a liquid can be tracked outside the pipe to locate leaks underground.
| Use | Radiation | Reason |
|---|---|---|
| Smoke alarm | Alpha | Ionises air; stopped by smoke |
| Paper thickness | Beta | Partly absorbed by thin sheets |
| Sterilising food | Gamma | Penetrates sealed packaging |
Section 3 of 5Why Half-Life Matters
1
A source for a smoke alarm must work for many years, so it has a long half-life, such as americium-241 at about 432 years.
2
A tracer in a pipe should not stay active for long, so a source with a half-life of hours or days is preferred.
3
A thickness gauge needs a stable reading over months, so its source must have a half-life of years.
4
The activity of a short half-life source falls quickly, which limits the exposure to people and to the environment.
5
Safe sources are sealed, shielded and handled with tongs so that users avoid contamination.
Section 4 of 5Benefits and Risks
Benefit
- Radiation allows non-destructive testing and sterilising that would be difficult or costly using chemicals or heat.
Risk to users
- Ionising radiation can damage cells, so workers wear dosimeter badges and limit time spent near sources.
Distance and shielding
- Increasing distance and using lead or concrete barriers reduce the dose from a source.
Disposal
- Used sources must be stored securely, because some stay radioactive for many years.
Section 5 of 5Exam Checklist & Tips
6.3.3 – Key Points for the Exam
- Ionising radiation Radiation, such as alpha, beta or gamma, that can remove electrons from atoms.
- Tracer A radioactive substance used to follow the path of a material through a system.
- Sterilising Killing microorganisms so that an item is safe to use or eat.
- Half-life The time taken for the activity of a source, or the number of unstable nuclei, to halve.
- Penetrating power How far radiation can pass through a material before it is absorbed.
Common Mistakes
- Saying gamma rays make food radioactive; irradiation does not make the food itself radioactive.
- Choosing an alpha source to measure the thickness of a metal sheet; alpha cannot pass through it.
- Choosing a source with a very short half-life for a smoke alarm, which then stops working quickly.
- Confusing contamination with irradiation, which is exposure to radiation without any radioactive material landing on you.