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AQA GCSE Physics · Topic 4.4 Atomic structure · Physics only
Edexcel International GCSE Physics · Section 7 Radioactivity and particles
Uses of Nuclear Radiation
Physics only This spec point is triple / physics only. If you are
sitting Combined Science (Trilogy), you can skip it.
In this lesson you'll learn to: choose the right radiation and half-life for a job, explain why monitors need a long half-life and tracers a short one, and explain how a smoke alarm, a thickness gauge and a medical tracer work.
In this lesson you'll learn to: choose the right radiation and half-life for a job, explain why monitors need a long half-life and tracers a short one, and explain how a smoke alarm, a thickness gauge and a medical tracer work.
In this lesson you'll learn to: describe the uses of ionising radiation in industry and
medicine — smoke alarms, thickness gauges, tracers, sterilising and radiotherapy — choosing the
right radiation and half-life for each, with a reason for both.
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Prefer to watch? Scroll to the bottom for the video on this topic
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A video walkthrough is coming soon — it will appear at the bottom of this page
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Start here — have a play
Don't read anything yet. On tab 1 you get five real jobs: a smoke alarm, a paper mill, a foil line, a patient and a leaking water pipe. For each one, choose the radiation and the half-life, then press Check. Get them wrong first; the explanation is the exam answer. Tab 2 shows why a smoke alarm and a medical tracer need opposite half-lives.
Job
Radiation
Half-life
The job, and your answer
Scored: 0 of 0 choices
Half-lives are the usual textbook values — enough for the exam, not a lab measurement.
▲ Every answer comes from two questions: what is the radiation supposed to get through, and does the source need to last or disappear?
Got the pattern? Now learn to write it.
These questions are nearly always "explain why this source is suitable". The marks come from naming the radiation with a reason and the half-life with a reason — never just one.
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Revision notes
Monitors need a LONG half-life
A monitor is a device that has to keep working: a smoke alarm, a thickness gauge. It works by comparing the count-rate now with the count-rate when nothing is in the way.
- A long half-life means the activity barely changes over months or years, so the source gives a constant count-rate to compare against.
- So if the count-rate decreases, you know it is because more radiation is being absorbed by the material — and not because the source has decayed.
- A short half-life would make the reading drift, and the monitor would give false readings.
Tracers need a SHORT half-life
A tracer is something you follow — through a body, a pipe or a river — and then want gone.
- A short half-life means the count-rate reduces to almost zero soon after the measurement, which limits harmful exposure to humans. The patient is not left radioactive.
- But it must still be long enough to travel to where it is going and be measured.
Choosing the radiation
⭐ The rule that decides every answer
Pick the radiation that is partly affected by the thing you are measuring — and, if the source is inside a body, the one that can get out.
| Use | Monitor or tracer? | Radiation | Half-life | Why |
|---|---|---|---|---|
| Smoke alarm | Monitor | Alpha | Long | Alpha ionises the air so a small current flows. Smoke absorbs the alpha, the current falls and the alarm sounds. Beta and gamma would pass straight through the smoke. Long half-life so the alarm still works in ten years. |
| Paper or foil thickness gauge | Monitor | Beta | Long | Beta is partly absorbed, so the count-rate changes with thickness: too thick and it falls, too thin and it rises, and the rollers adjust. Alpha would be stopped completely and gamma would pass straight through. |
| Medical tracer (technetium-99m) | Tracer | Gamma | Short (6 hours) | Only gamma is penetrating enough to escape the body and reach the detector. Short half-life so the patient's exposure is small. |
| Leak in a water pipe near the surface | Tracer | Beta | Short | Where the pipe is sound the beta is absorbed; where there is a crack the water carries the tracer out and the count-rate above ground jumps. A pipe buried deep needs gamma instead. |
More uses in medicine and industry
| Use | Radiation | How it works |
|---|---|---|
| Sterilising medical equipment and food | Gamma | Gamma passes through the sealed packaging and kills bacteria. The equipment or food does not become radioactive. |
| Radiotherapy (treating cancer) | Gamma | Beams of gamma from several directions meet at the tumour and kill the cancer cells, while each beam on its own does less damage to healthy tissue. |
| Tracers in medicine (technetium-99m) | Gamma | Injected, then followed round the body with a gamma camera to find a blockage or a tumour. |
Risk and benefit
Radiation damages cells, so every use carries a risk. A medical tracer does give the patient a dose — but the scan finds a problem that could not be found otherwise, so the benefit outweighs the risk. The short half-life and the small quantity used keep that risk as low as possible.
The people who work with sources are protected the same way as in any lab: distance and time to reduce irradiation, and gloves and tongs to prevent contamination.
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How it comes up in the exam
“Explain why this source is suitable.” Two parts, two reasons.
It emits [radiation], which [what it can or can't get through],
so [what that lets the device do]. It has a [long / short]
half-life, so [constant count rate / count rate falls to almost zero], so
[the reading only changes because of … / exposure to people is limited].
the property what it does why that matters
Exam-style question · 4 marks
A paper mill uses a beta source with a half-life of 30 years to check the thickness of the paper. Explain why this source is suitable.
- Beta is partly absorbed by the paper (1), so the count rate changes with the thickness: thicker paper, lower count rate (1)
- A half-life of 30 years is long, so the count rate stays constant (1)
- so any change in the reading is caused by the thickness, not by the source decaying (1)
No mark: “alpha would be stopped” on its own. Say what beta does that makes it right.
Exam-style question · 4 marks
A hospital uses technetium-99m as a tracer. It emits gamma radiation and has a half-life of 6 hours. Explain why these two properties make it suitable.
- Gamma is very penetrating (1), so it can pass out of the patient's body and be detected outside (1)
- A half-life of 6 hours is short, so the count-rate falls to almost nothing soon after the scan (1)
- which limits the patient's exposure — but it is still long enough to travel round the body and be imaged (1)
Marking note: "because gamma is best" scores nothing. Every mark needs the property and what it lets you do.
📘 Now do it in your workbook
Explain why monitors need a long half-life and tracers a short one, using the key words, then annotate the smoke alarm, the technetium-99m scan and the paper thickness monitor.
AQA GCSE Physics Workbook · ATOMIC STRUCTURE · page 13 Physics only Edexcel iGCSE Physics Workbook · RADIOACTIVITY AND PARTICLES · page 11✅ Can you do it? Tick as you go
0% complete🎉 Nice work! You've ticked off every objective for this spec point.
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Prefer to watch? Here's the whole thing
Video walkthrough — coming soon
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it.
Everything above, explained out loud — useful for a last-minute recap, or if you'd rather hear it than read it. The video is on its way.
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Video coming soon
The walkthrough for this lesson is being filmed and will appear right here. Until then, the animation and the notes above cover every mark.
Now put it into practice
Page 13 of the workbook: monitors, tracers and three real uses to annotate in your own words.
Page 11 of the workbook: monitors, tracers and three real uses to annotate in your own words.
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