Background radiation — AQA GCSE Physics
Test yourself on Background radiation with AQA GCSE practice questions.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Background radiation explained
Background radiation is the low level of ionising radiation present everywhere, all the time.
Read the full explanation
Most of it is natural. Radon gas seeps out of rocks, especially granite, and is breathed in; cosmic rays arrive from space and are partly absorbed by the atmosphere; there are naturally radioactive isotopes in soil, building materials, food and drink, and in our own bodies. A smaller share is man-made, chiefly fallout from nuclear weapons testing and from nuclear accidents, plus medical procedures and waste from the nuclear industry. Because it never switches off, every experiment with a source has to start by measuring the count rate with no source present and subtracting that background from every reading.
The level of background radiation and radiation dose may be affected by occupation and/or location.
Not everyone receives the same dose. Location matters because rock type and altitude vary: houses built on granite, as in parts of Cornwall and Aberdeen, receive far more radon than those on chalk or clay, and at high altitude there is less atmosphere above you to absorb cosmic rays. Occupation matters because some jobs put people near sources: radiographers and radiotherapy staff, workers in nuclear power stations and reprocessing plants, and aircrew who spend working hours at altitude. These workers are monitored with film badges or electronic dosimeters and work to legal dose limits, because a higher dose raises the chance of damage to cells and DNA and so of cancer developing later.
Radiation dose is measured in sieverts (Sv) 1000 millisieverts (mSv) = 1 sievert (Sv) Students will not need to recall the unit of radiation dose.
Radiation dose measures the risk of harm to body tissue from being exposed to radiation, taking account of both the amount of radiation absorbed and how damaging that type is. It is measured in sieverts, symbol Sv, and because a sievert is a large dose most everyday figures appear in millisieverts, with 1000 mSv = 1 Sv. So a typical UK annual background dose of about 2.7 mSv is 0.0027 Sv. Dose is not the same as activity: activity in becquerels counts decays per second in the source, while dose describes what the exposed person actually receives. The specification says you will not have to recall the unit, so it will be given; what you do need is to compare and convert the figures supplied.
Your focus
- Name two natural and one man-made source of background radiation.
- Describe how a background count rate is measured and used to correct readings from a source.
- Interpret a count-rate against distance graph that levels off, identifying the level as background.
Show all 9 objectives
- Name an occupation and a location that raise a person's annual radiation dose, giving the reason in each case.
- Explain why a house built on granite has a higher indoor radon level than one built on clay.
- Describe how workers' doses are monitored and limited.
- Convert between millisieverts and sieverts in both directions.
- Distinguish radiation dose in sieverts from source activity in becquerels.
- Compare two quoted doses and state which carries the greater risk of harm.
Background radiation exam tips
Marking Points
- one mark for background radiation being present all the time, from many sources around us
- one mark for two named natural sources, such as radon from rocks, cosmic rays from space, or food and drink
- one mark for a named man-made source, such as fallout from nuclear weapons testing or from a nuclear accident
- one mark for measuring the count rate with no source present and subtracting it from each reading
- one mark for a named occupation with a raised dose, such as radiographer, nuclear industry worker or aircrew
- one mark for a named location factor, such as granite areas releasing radon or high altitude reducing the absorption of cosmic rays
- one mark for linking a higher dose to a greater risk of damage to cells or of developing cancer
- one mark for a control measure such as a film badge or dosimeter and a legal dose limit
- one mark for radiation dose being measured in sieverts, with 1000 millisieverts equal to 1 sievert
- one mark for a correct conversion, such as 2.7 mSv written as 0.0027 Sv
- one mark for recognising that dose measures the risk of harm to tissue rather than the number of decays per second
- one mark for a comparison made using the figures given in the question rather than recalled values
Examiner Tips
- 💡Check whether the question asks for natural or man-made sources, because a correct example from the wrong category scores nothing.
- 💡In range experiments, quote the background count rate as the level the readings fall back to; examiners look for that phrase.
- 💡Give a specific source, such as radon from granite, rather than a category like 'the environment'.
- 💡Name the occupation and the reason together; the job title alone is usually only half the answer.
- 💡If a data table of doses is given, quote figures from it rather than recalled values.
- 💡Say 'more radon' or 'more cosmic rays' explicitly when explaining a location effect.
- 💡Convert every value to the same unit before you compare doses, and write the converted values down.
- 💡Watch for the prefix; mSv and Sv differ by a factor of one thousand and the numbers look deceptively similar.
- 💡Quote the dose figures from the stem in your conclusion so the examiner can see the comparison you made.
Common Mistakes
- listing only man-made sources and treating background radiation as pollution
- giving 'the Sun' as a source rather than cosmic rays from space
- claiming radon comes from nuclear power stations rather than from rocks
- forgetting the background correction, so the count rate appears not to fall to the expected level
- saying background radiation is zero indoors
- explaining aircrew doses by saying they are closer to the Sun's heat rather than less shielded from cosmic rays
- assuming everyone in the country receives an identical dose
- confusing dose in sieverts with the activity of a source in becquerels
- treating radon as a man-made pollutant
- naming an occupation with no reason why the dose is higher
- quoting a dose in becquerels, which is the unit of activity
- multiplying by 1000 when converting millisieverts to sieverts instead of dividing
- treating a large dose and a large activity as necessarily the same thing
- comparing a dose in mSv with one in Sv without converting first
- spending time trying to recall the unit when the specification says it will be provided