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Physics · Atomic structure

Radioactive contamination and irradiation

Distinguish contamination from irradiation, compare their hazards, and describe precautions and the role of peer review.

  • 6 key terms
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Teacher resources

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Student handouts

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Warm-up

Answer each one, then check.

  1. 1

    What is ionising radiation?

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    Radiation that can knock electrons off atoms

  2. 2

    What are alpha, beta and gamma?

    Show answerHide answer

    Types of nuclear radiation

  3. 3

    Which radiation is most penetrating?

    Show answerHide answer

    Gamma

  4. 4

    What is a hazard?

    Show answerHide answer

    Something that could cause harm

  5. 5

    What does peer review mean?

    Show answerHide answer

    Checking by other scientists before results are accepted

Learning Objectives

  1. 1Define radioactive contamination and irradiation.
  2. 2Compare the hazards of contamination and irradiation.
  3. 3Describe precautions when handling sources.
  4. 4Explain why studies on the effects of radiation are published and peer reviewed.

CONTAMINATION vs IRRADIATION

Radioactive contamination is the unwanted presence of materials containing radioactive atoms on other materials. Irradiation is exposing an object to nuclear radiation: the irradiated object does not become radioactive.

The hazard from contamination is due to the decay of the contaminating atoms; the type of radiation emitted affects the level of hazard.

Which Is More Hazardous?

Irradiation

  • The object is exposed from outside.
  • It stops when the source is removed or shielded.
  • The object does not become radioactive.
  • Hazard depends on the type of radiation and time exposed.

Contamination

  • Radioactive atoms are on or in the object.
  • Radiation continues until the atoms decay or are removed.
  • Alpha sources inside the body are very dangerous.
  • Can spread to other objects.

Precautions When Using Sources

Protect against irradiation and contamination.

  1. 1 Distance

    Handle sources with tongs; keep away.
  2. 2 Time

    Keep exposure times short.
  3. 3 Shielding

    Store sources in lead-lined containers.
  4. 4 Protective clothing

    Gloves and coats stop contamination.
  5. 5 Hygiene

    No eating or drinking; wash hands.

Comparing Hazards

Explain why an alpha source is not very hazardous outside the body but is very hazardous if swallowed.

Show the solutionHide the solution
  1. 1 Outside Alpha is stopped by air, paper or skin
  2. 2 Inside Contamination puts the source in contact with living cells
  3. 3 Ionising Alpha is strongly ionising and damages cells

AnswerOutside, alpha cannot penetrate skin; inside it is contamination and its strong ionising damages cells.

Peer Review

Why it matters.

  • Publish and share

    Findings on the effects of radiation on humans must be published so that other scientists can check them.

  • Peer review

    Other scientists check the methods and conclusions before they are accepted.

  • Trust

    This makes conclusions more reliable and helps set safety rules.

Compare the Hazards

A worker handles a gamma source with tongs and a worker accidentally spills a solution containing radioactive iodine on their skin. Say which is irradiation and which is contamination, and compare the hazards.

1. Name each.

2. Compare how long exposure lasts.

A good answer shows: The gamma source: irradiation (they are exposed while nearby, they do not become radioactive). The spill: contamination (radioactive atoms are on the skin and keep decaying). Contamination can continue and be spread or absorbed, so is more serious unless removed.

Can I...?

  1. 1Define contamination.
  2. 2Define irradiation.
  3. 3Explain irradiated objects are not radioactive.
  4. 4Compare the hazards.
  5. 5Give precautions.
  6. 6Explain why peer review matters.
  7. 7Explain why alpha is dangerous inside the body.
  8. 8Choose safe handling.

Summary & Exam Focus

  • Contamination: radioactive atoms on or in the object.
  • Irradiation: exposed to radiation; not radioactive.
  • Hazard depends on the type of radiation.
  • Peer review checks findings.

Exam focus

State the difference between contamination and irradiation. (2 marks) (2 marks)

Contamination involves radioactive atoms on the object; irradiation is exposure without the object becoming radioactive.

Key terms

The vocabulary this lesson expects you to use. Each one is linked from the first place it appears above.

Contamination
The unwanted presence of radioactive atoms on or in other materials.
Irradiation
Exposure to nuclear radiation without radioactive atoms being transferred.
Shielding
Material used to absorb radiation.
Peer review
Checking of scientific work by other scientists.
Hazard
Something that could cause harm.
Precaution
An action to reduce a risk.

Questions and answers

10 questions set on this lesson, with the mark schemes and model answers open.

1. Exam question State 2 marks Easier

Explain the difference between radioactive contamination and irradiation.

Mark scheme — 2 marks available

  • Contamination: radioactive atoms present on other materials — 1 mark
  • Irradiation: exposure and the object does not become radioactive — 1 mark

Model answer

Contamination is the unwanted presence of radioactive atoms on or in another material. Irradiation is exposing an object to radiation; the object does not become radioactive.

2. Exam question Explain 3 marks Easier

A student says that a person who has been irradiated by a gamma source is now radioactive. Explain why the student is wrong.

Mark scheme — 3 marks available

  • Irradiation is exposure — 1 mark
  • No radioactive atoms transferred — 1 mark
  • So the person is not radioactive — 1 mark

Model answer

Irradiation means exposure to radiation from outside. The person has not received radioactive atoms, so they do not become radioactive.

3. Exam question Suggest 2 marks Easier

Give two precautions that should be taken when a teacher handles a radioactive source.

Mark scheme — 2 marks available

  • First precaution — 1 mark
  • Second precaution — 1 mark

Model answer

Any two from: use tongs; keep the source in a lead-lined box; keep exposure time short; keep away from the body; wear gloves.

4. Exam question Compare 3 marks Easier

Compare the hazards of contamination and irradiation from an alpha source.

Mark scheme — 3 marks available

  • Irradiation by alpha: low hazard, absorbed — 1 mark
  • Contamination inside the body: high hazard — 1 mark
  • Alpha strongly ionising — 1 mark

Model answer

Outside the body, irradiation by alpha is not hazardous because alpha is absorbed by air or skin. If contamination puts the alpha source inside the body it is very hazardous because alpha is strongly ionising and damages cells.

5. Exam question Explain 2 marks Easier

Scientists who study the effects of radiation on humans publish their findings. Explain why it is important that the findings are peer reviewed.

Mark scheme — 2 marks available

  • Findings checked by other scientists — 1 mark
  • So more reliable or valid — 1 mark

Model answer

Other scientists can check the methods and conclusions, so the results are more reliable.

6. Multiple choice 1 mark Easier

Irradiation means the object is...

  1. A made radioactive
  2. B cooled
  3. C heated
  4. D exposed to radiation Correct

Why: It does not become radioactive.

7. Multiple choice 1 mark Core

Contamination means radioactive atoms are...

  1. A on or in the object Correct
  2. B absent
  3. C only in the source
  4. D only in the air

Why: They keep decaying.

8. Multiple choice 1 mark Core

Which reduces the danger from a source?

  1. A Holding it near
  2. B Using tongs Correct
  3. C Removing shielding
  4. D Longer exposure

Why: It increases the distance.

9. Multiple choice 1 mark Core

An alpha source is most dangerous...

  1. A in a lead box
  2. B in a drawer
  3. C inside the body Correct
  4. D on a shelf

Why: It ionises cells directly.

10. Multiple choice 1 mark Stretch

Peer review means...

  1. A the results are secret
  2. B one person decides
  3. C the work is ignored
  4. D other scientists check the work Correct

Why: It helps to ensure reliability.