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Physics · Atomic structure

Background radiation

Describe the natural and man-made sources of background radiation, and explain how radiation dose can vary with occupation and location.

  • 6 key terms
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Warm-up

Answer each one, then check.

  1. 1

    What is radiation?

    Show answerHide answer

    Energy emitted as waves or particles

  2. 2

    Name a rock that contains radioactive material.

    Show answerHide answer

    Granite

  3. 3

    What does mSv stand for?

    Show answerHide answer

    Millisievert

  4. 4

    Where do cosmic rays come from?

    Show answerHide answer

    Space

  5. 5

    What is a Geiger-Müller tube?

    Show answerHide answer

    A detector of radiation

Learning Objectives

  1. 1Describe the sources of background radiation.
  2. 2Explain why radiation dose varies with location and occupation.
  3. 3Use data on radiation dose in millisieverts.

BACKGROUND RADIATION

Background radiation is around us all of the time. It comes from natural sources such as rocks and cosmic rays and from man-made sources such as fallout from nuclear weapon tests and accidents.

Radiation dose is measured in sieverts (Sv). 1000 millisieverts (mSv) = 1 sievert. You do not need to recall the unit.

Where Does It Come From?

  • Natural: rocks

    Radioactive isotopes in rocks such as granite release radon gas.

  • Natural: cosmic rays

    High-energy particles from space; stronger at altitude.

  • Natural: food and air

    Small amounts in food, drink and the air.

  • Man-made

    Fallout from nuclear weapon testing and accidents, and medical procedures.

Why Dose Varies

Location and occupation.

  • Location

    Effect: Areas with granite rock have higher radon levels; high altitudes have more cosmic rays.

  • Occupation

    Effect: Airline crews (cosmic rays), radiographers and nuclear workers receive higher doses.

  • Medical treatments

    Effect: X-rays and scans add to a person's dose.

Using a Pie Chart

The typical annual dose is 2.7 mSv. Radon is 50% of this. Calculate the dose from radon.

Show the solutionHide the solution
  1. 1 Fraction \(50\% = 0.50\)
  2. 2 Multiply \(0.50 \times 2.7\)
  3. 3 Answer \(1.35\) mSv

Answer1.35 mSv (about 1.4 mSv)

Converting Units

Convert 2.7 mSv to sieverts.

Show the solutionHide the solution
  1. 1 1000 mSv = 1 Sv \(2.7 \div 1000\)
  2. 2 Answer \(0.0027\) Sv (2.7 × 10⁻³ Sv)

Answer\(2.7 \times 10^{-3}\) Sv

Measuring It

How background is found.

  • Detector

    A Geiger-Müller tube and counter measures the count rate.

  • Correct

    Subtract the background count rate from measurements on a source.

  • Vary

    Background changes with place and time, so measure it in the same place.

Why Does It Differ?

Explain why the background radiation is higher in Cornwall (granite) than in London, and why an airline pilot receives a higher dose than an office worker.

1. Name the source.

2. Link it to location or job.

A good answer shows: Granite rocks contain radioactive isotopes and release radon gas, so background is higher. Pilots fly at high altitude where there are more cosmic rays.

Can I...?

  1. 1List natural sources.
  2. 2List man-made sources.
  3. 3Explain location effects.
  4. 4Explain occupation effects.
  5. 5Use a pie chart.
  6. 6Convert mSv to Sv.
  7. 7Correct for background.
  8. 8Explain why background varies.

Summary & Exam Focus

  • Natural: rocks, cosmic rays, food.
  • Man-made: fallout, medical procedures.
  • Dose varies with location and occupation.
  • 1000 mSv = 1 Sv.

Exam focus

Give two natural sources of background radiation. (2 marks) (2 marks)

Any two: rocks, cosmic rays, food.

Key terms

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

Background radiation
Radiation that is around us all the time.
Cosmic rays
High-energy particles from space.
Radon
A radioactive gas from rocks.
Radiation dose
A measure of the risk of harm from radiation, in sieverts.
Millisievert
One thousandth of a sievert.
Man-made
Produced by human activity.

Practice questions

Have a go at each one before you open its answer.

  1. Question 1 State 2 marks

    Give two natural sources of background radiation.

    Show answerHide answer

    Model answer

    Any two from: rocks (including radon gas), cosmic rays, food and drink.

    Mark scheme

    • First source — 1 mark
    • Second source — 1 mark
  2. Question 2 State 2 marks

    Give one man-made source of background radiation.

    Show answerHide answer

    Model answer

    Fallout from nuclear weapons testing or nuclear accidents (or medical procedures).

    Mark scheme

    • One correct source — 1 mark
    • Man-made linked to human activity — 1 mark
  3. Question 3 Use the chart 3 marks

    The pie chart shows the sources of background radiation. The total annual dose is 2.7 mSv. Radon is 50% of the total. (a) Calculate the dose from radon. (b) Is most of the background radiation natural or man-made? Give a reason.

    A pie chart of the sources of background radiation with radon as the largest sector.
    Show answerHide answer

    Model answer

    (a) 0.50 × 2.7 = 1.35 mSv. (b) Natural, because the natural sources (radon, ground, food, cosmic rays) make up most of the chart.

    Mark scheme

    • 1.35 mSv — 1 mark
    • Natural — 1 mark
    • Reason from the chart — 1 mark
  4. Question 4 Explain 2 marks

    The background radiation is higher in some parts of the UK than others. Suggest one reason.

    Show answerHide answer

    Model answer

    Some areas have rocks such as granite that contain radioactive isotopes and release radon gas.

    Mark scheme

    • Type of rock or radon — 1 mark
    • Linked to higher levels in that location — 1 mark
  5. Question 5 Explain 3 marks

    Airline pilots receive a higher radiation dose than office workers. Explain why. Also state how background radiation is taken into account when measuring the radiation from a radioactive source.

    Show answerHide answer

    Model answer

    Pilots fly at high altitude where cosmic rays are stronger. The background count rate is measured without the source and subtracted from the reading with the source.

    Mark scheme

    • Cosmic rays at altitude — 1 mark
    • Measure background count rate — 1 mark
    • Subtract from the reading — 1 mark

Quick check

  1. Which is a natural source of background radiation?

    1. ACosmic rays
    2. BNuclear weapons fallout
    3. CX-rays in hospital
    4. DNuclear power stations
    Show answerHide answer

    A: Cosmic rays

    They come from space.

  2. Radon gas comes from...

    1. Athe Sun
    2. Brocks
    3. Cbatteries
    4. Dfood only
    Show answerHide answer

    B: rocks

    It is released by some rocks.

  3. Radiation dose is measured in...

    1. Abecquerel
    2. Bjoules
    3. Csieverts
    4. Dwatts
    Show answerHide answer

    C: sieverts

    1 Sv = 1000 mSv.

  4. Which job usually gives a higher dose?

    1. ALibrarian
    2. BWaiter
    3. CTeacher
    4. DAirline pilot
    Show answerHide answer

    D: Airline pilot

    Higher cosmic ray exposure.

  5. 1000 mSv equals...

    1. A1 Sv
    2. B1 mSv
    3. C10 Sv
    4. D0.1 Sv
    Show answerHide answer

    A: 1 Sv

    1000 milli = 1.

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