Edexcel IGCSE Physics · Spec 7.15-7.16
Irradiation, Contamination and Radioactive Waste
Covers distinguish irradiation from contamination, Choose controls for each hazard and Explain radioactive-waste disposal problems.
Physics revision video
Irradiation, Contamination and Radioactive Waste
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Explained
Irradiation, contamination, and why the difference matters
These two words are often used interchangeably in everyday speech, and in physics they mean opposite situations. Irradiation is being exposed to radiation from a source outside you. Contamination is having radioactive material on you or inside you. Get that distinction right and the rest of the topic follows.
Irradiation
Irradiation is exposure to ionising radiation from an external source. The important consequence is that the object does not become radioactive. Once you move away from the source, or the source is removed, the exposure stops.
This is why irradiation is used to sterilise medical instruments and some foods. The radiation kills bacteria, and the instrument is not left radioactive afterwards, so it is safe to use.
Contamination
Contamination means unwanted radioactive material is on or inside an object. Removing yourself from the area does not help, because the source has come with you. It continues to emit radiation until it decays or is physically removed.
Contamination inside the body is the more dangerous of the two, because alpha radiation, which is easily stopped by skin from outside, is highly ionising once it is already within tissue.
Choosing the right control
Because the hazards are different, the precautions are different, and questions reward matching the control to the hazard.
- Against irradiation: increase distance from the source, reduce exposure time, and use shielding such as lead or thick concrete.
- Against contamination: contain the source, use sealed containers, wear gloves and protective clothing, and handle material with tongs so it cannot transfer.
What examiners say about this topic
Principal examiner reports for Edexcel International GCSE Physics record limited understanding of the difference between contamination and irradiation, with some learners gaining marks by listing multiple safety precautions that were not always relevant.
That is a warning worth taking seriously. Listing every precaution you can think of is not a strategy. Decide which hazard the question describes, then give the precautions that address that hazard.
Reports on the wider topic also note that many responses gave examples of ionising radiation rather than explaining what the term means. If asked what ionising radiation is, say that it removes electrons from atoms or molecules. Naming alpha, beta and gamma answers a different question.
Radioactive waste
Waste has to be dealt with for both hazards at once. It must be contained so that material cannot escape and contaminate anything, and shielded so that workers and the public are not irradiated by it.
The difficulty is time. Some waste stays dangerously radioactive for thousands of years, which is longer than any building or institution has ever lasted. That is why deep geological storage is proposed, and why the problem is as much political as scientific.
Spec 7.15-7.16
What you need to know
- Distinguish irradiation from contamination
- Choose controls for each hazard
- Explain radioactive-waste disposal problems
Active recall
Quick check
Answer each question before opening the answer.
Does irradiation transfer radioactive material?
No
Why is internal alpha contamination dangerous?
Alpha is strongly ionising inside the body
Why is long-lived waste difficult?
It requires secure containment for very long periods
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