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AQA GCSE Physics · Topic 4.4 Atomic structure
7.15 · 7.16
Edexcel International GCSE Physics · Section 7 Radioactivity and particles
Radioactive Contamination and Irradiation
In this lesson you'll learn to: tell irradiation and contamination apart, give the
two ways to reduce each one — distance and time for irradiation, gloves and
tongs for contamination — explain why alpha is the safest outside the body and the most
dangerous inside it, write the chain that explains why radiation is dangerous, and (depending on your board) say
why findings are peer reviewed or how radioactive waste is disposed of safely.
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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 scene 1, take the source out on the short-handled tongs and watch the dose race up — then reset, pick up the long-handled tongs, and do it again. On scene 2, put the isotope on the skin with alpha selected, then swallow it: the same radiation goes from the safest to the most dangerous. Scene 3 gives you six scenarios to sort.
Distance
Dose rate: 0 units/s
Total dose: 0 units
What's happening
Dose is shown in arbitrary units, so you can compare the three choices — the real numbers are not on the spec.
▲ Irradiation stops the moment the source is back in the box. Contamination does not — it goes where the person goes.
Now learn the wording that scores.
This topic is almost all written answers, and the examiner is looking for particular words. The notes below give you both definitions, the two ways to reduce each, and the exact sentences that earn the marks.
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Revision notes
Irradiation
Irradiation is when an object or person is exposed to ionising radiation — alpha, beta or gamma — from a source outside them. The radiation reaches them, but the radioactive material itself never touches them.
⭐ Key fact — irradiation does NOT make something radioactive
The nuclear radiation is either absorbed by the object or passes through it — and that is the end of it. The radiation stops as soon as the source is removed or put back in its lead-lined box. This is the single most-tested sentence in the topic.
The two ways to reduce irradiation
| Reduce it by… | How | Why it works |
|---|---|---|
| Increasing the distance | Use long-handled tongs to hold the source, and stand (or keep the class) further away. | The radiation spreads out, so much less of it reaches you. Double the distance and the dose rate drops to about a quarter. |
| Decreasing the time | Have the source out for as short a time as possible, then put it straight back into the lead-lined box. | Total dose = dose rate × time, so half the time means half the dose. |
Lead shielding is a third way — and in a school lab that means the lead-lined box the source is stored in, which is where the animation starts. (Lead aprons and lead screens belong in a hospital; nobody is wearing lead in a classroom.) But if a question says "two ways", give distance and time.
Contamination
Contamination is when a radioactive isotope gets on or into a person or object. Now the radioactive atoms themselves are there, so the object does have the radioactive material on it or in it, and it keeps decaying until the isotope is removed or has decayed away.
You cannot walk away from contamination, because it travels with you. That is the whole difference.
The two ways to reduce contamination — both stop you touching it
| Reduce it by… | Why it works |
|---|---|
| Using tongs to handle the source, never bare hands | Nothing from the source can get onto your skin. |
| Wearing plastic gloves (and washing your hands afterwards) | The gloves take the isotope instead of your skin, and are then removed and disposed of safely. |
💡 These score nothing for contamination
"Wear a lead apron" and "wear goggles" stop radiation reaching you — they do not stop radioactive material landing on you. "Stand further away" is an irradiation answer: once you are contaminated, distance is useless, because the isotope moved with you.
⭐ The difference examiners look for
Irradiation does not make an object radioactive — the nuclear radiation is absorbed or transmitted, and the irradiation ends when the source is removed. Contamination does have a radioactive source on an object, or in it, so it keeps decaying and travels with it.
That is why gloves and tongs matter for contamination, but distance and time matter for irradiation.
Alpha, beta and gamma: it depends where the source is
Which radiation is most dangerous has no single answer — you must say inside or outside the body first. This catches people out every year.
| Outside the body | Inside the body (contamination) | |
|---|---|---|
| Alpha | Least harmful. It is stopped by the dead outer layer of skin (or a few cm of air), so hardly any reaches living cells. | Most harmful. The skin can't protect anything now. Alpha is very strongly ionising and travels only a short way, so it ionises the atoms and mutates the cells right next to it. |
| Beta | In between — it passes through skin and reaches the tissue underneath. | In between — less strongly ionising than alpha, and the damage is spread out. |
| Gamma | Most harmful. Very penetrating — it is the only nuclear radiation that can pass into the centre of the body, so it can ionise atoms and mutate cells in people's organs. | Least harmful. Weakly ionising, and so penetrating that most of it passes straight back out of the body. |
Why is radiation dangerous?
Learn this as a chain, and write it as a chain:
⭐ The damage chain
nuclear radiation → ionises atoms → mutates cells → can cause cancer
A high dose can kill cells outright, which causes radiation sickness. A lower dose is more likely to damage the DNA so the cell still lives but divides out of control.
Risk versus benefit
Radiation is still used in hospitals every day, because the benefit to the patient outweighs the small extra risk:
- Radiotherapy kills cancer cells, so a small extra dose is worth it to treat a tumour.
- Medical tracers and X-rays give a diagnosis that could not be made any other way.
- Sterilising surgical instruments with gamma prevents infection.
AQA only⭐ Published findings and peer review
Studies into the effects of radiation on humans must be published and shared with other scientists, so the findings can be checked by peer review. That is how results are tested for mistakes and bias before anyone relies on them — and it is a marked point on this spec statement.
Edexcel onlyDisposing of radioactive waste
Used fuel from nuclear power stations, and anything that has been contaminated (gloves, clothing, equipment), is radioactive waste. The problems with getting rid of it:
- Some isotopes in it have very long half-lives, so the waste stays dangerous for thousands of years.
- If a container leaks, the waste can contaminate the ground, water supplies and food chains.
- It must be kept secure, so nobody can steal it or come across it by accident.
How the risks are reduced:
- Low-level waste (gloves, protective clothing) is sealed in containers and buried in specially lined sites.
- High-level waste (used fuel) is cooled under water first, then sealed in glass inside steel and concrete containers, and stored deep underground in stable rock, where it is monitored.
⭐ The answer that gets the marks
Problem: radioactive waste has a long half-life, so it stays radioactive for a very long time and could contaminate water or land if it leaks. Solution: seal it in strong containers and store it deep underground, away from people, where it can be monitored.
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How it comes up in the exam
The big one is a 5- or 6-mark "describe how to reduce the danger" question. Tick off these five words as you write, and you will not miss a mark: irradiation · contamination · distance · time · touch.
Exam-style question · 5 marks
A school technician takes a radioactive source out of its lead-lined box to use in a lesson. Describe how the technician can reduce the danger to themselves and to the students.
Mark scheme — any five:
- Hold the source with long-handled tongs to increase the distance — this reduces irradiation (1)
- Keep the source out for the shortest time possible, then return it to its lead-lined box (1)
- Never touch the source with bare hands — this prevents contamination (1)
- Wear plastic gloves, and wash hands afterwards (1)
- Keep the students far away / point the source away from people (1)
- Store the source in a lead-lined box whenever it is not in use (1)
Where the marks go: each point needs the action and the reason. "Use tongs" on its own is worth less than "use tongs to increase the distance from the source".
Exam-style question · 2 marks
A worker spills a liquid containing an alpha-emitting isotope on their hand. Explain why this is more dangerous if the worker then eats lunch without washing their hands.
On the skin, alpha is stopped by the dead outer layer, so it does little damage (1). If it is swallowed it is inside the body, where alpha is very strongly ionising and dumps all its energy into nearby living cells, which can mutate and cause cancer (1).
📘 Now do it in your workbook
Fill in both definitions, the two ways to reduce each, and the 5-mark technician question — then mark your own answer against the mark scheme at the back.
AQA GCSE Physics Workbook · ATOMIC STRUCTURE · page 11 Edexcel iGCSE Physics Workbook · RADIOACTIVITY AND PARTICLES · page 12
⬇ Free: page 11 (PDF)
📄 Full workbook PDF · £2.99
Paperback on Amazon
⬇ Free: page 12 (PDF)
📄 Full workbook PDF · £2.99
Paperback on Amazon
Free sample = the page for this lesson. The full workbook covers the whole of Topic 4 Atomic Structure, with exam-style questions and worked answers.
Free sample = the page for this lesson. The full workbook covers the whole of Section 7 Radioactivity and Particles, with exam-style questions and worked answers.
✅ Can you do it? Tick as you go
0% complete🎉 Nice work! You've ticked off every objective for this spec point.
Don't forget to hit “Mark complete” at the bottom of the lesson.
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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
Watching is the easy bit. Page 11 of the workbook makes you write both definitions and the 5-mark technician answer in your own words, with the mark scheme to check yourself against.
Watching is the easy bit. Page 12 of the workbook makes you write both definitions and the 5-mark technician answer in your own words, with the mark scheme to check yourself against.
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