Background Radiation (Edexcel International A Level Physics)

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Katie M


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Background Radiation

  • Radiation is a natural phenomenon, with radioactive elements having always existed on Earth and in outer space
    • However, human activity has added to the amount of radiation that humans are exposed to in various ways

  • Background radiation is defined as:

Low levels of radiation from environmental sources, which are always present around us

  • Radiation is measured in counts per second in a unit called Becquerel (Bq)

  • Different amounts of radiation are present in different places around the world, including in the UK. 


  • There are two types of background radiation:
    • Natural sources
    • Man-made sources

Background Radiation Chart, downloadable AS & A Level Physics revision notes

Background radiation is the radiation that is present all around the environment. Radon gas is given off from some types of rock

  • Every second of the day there is some radiation emanating from natural sources such as:
    • Rocks
    • Cosmic rays from space
    • Foods

Natural Sources

  • Radon gas from rocks and soil
    • Heavy radioactive elements, such as uranium and thorium, occur naturally in rocks in the ground
    • Uranium decays into radon gas, which is an alpha emitter
    • This is particularly dangerous if inhaled into the lungs in large quantities

  • Cosmic rays from space
    • The sun emits an enormous number of protons every second
    • Some of these enter the Earth’s atmosphere at high speeds
    • When they collide with molecules in the air, this leads to the production of gamma radiation
    • Other sources of cosmic rays are supernovae and other high energy cosmic events

  • Carbon-14 in biological material
    • All organic matter contains a tiny amount of carbon-14
    • Living plants and animals constantly replace the supply of carbon in their systems hence the amount of carbon-14 in the system stays almost constant

  • Radioactive material in food and drink
    • Naturally occurring radioactive elements can get into food and water since they are in contact with rocks and soil containing these elements
    • Some foods contain higher amounts such as potassium-40 in bananas
    • However, the amount of radioactive material is minuscule and is not a cause for concern

Man-Made Sources

  • Medical sources
    • In medicine, radiation is commonly used in X-rays, CT scans, radioactive tracers, and radiation therapy

  • Nuclear waste
    • While nuclear waste itself does not contribute much to background radiation, it can be dangerous for the people handling it

  • Nuclear fallout from nuclear weapons
    • Fallout is the residue radioactive material that is thrown into the air after a nuclear explosion, such as the bomb that exploded at Hiroshima
    • While the amount of fallout in the environment is presently very low, it increases significantly in areas where nuclear weapons are tested

  • Nuclear accidents
    • Accidents such as that in Chernobyl contributed a large dose of radiation into the environment
    • While these accidents are now extremely rare, they can be catastrophic

Corrected Count Rate

  • Background radiation must be accounted for when taking readings in a laboratory
  • This can be done by taking readings with no radioactive source present and then subtracting this from readings with the source present
    • This is known as the corrected count rate

Detecting Radiation

  • When alpha or beta radiation pass close to an atom, they can deliver enough energy to remove electrons, ionising the atom
  • Radiation detectors work by detecting the presence of either these ions, or the chemical changes that they produce
  • Examples of radiation detectors include:
    • Photographic film (often used in badges)
    • Geiger-Muller (GM) tubes
    • Ionisation chambers
    • Scintillation counters
    • Spark counters

Geiger-Counter, IGCSE & GCSE Physics revision notes

A Geiger-Muller tube (or Geiger counter) is a common type of radiation detector


Worked example

A student is using a Geiger-counter to measure the counts per minute at different distances from a source of radiation. Their results and a graph of the results are shown here.

Background example, downloadable IGCSE & GCSE Physics revision notes

Determine the background radiation count.

Step 1: Determine the point at which the source radiation stops being detected

    • The background radiation is the amount of radiation received all the time
    • When the source and detector are far enough apart, the radiation is absorbed by the air before reaching the Geiger-counter
    • Results after 1 metre should not change
    • Therefore, the amount after 1 metre is only due to background radiation

Step 2: State the background radiation count 

    • The background radiation count is 15 counts per minute

Exam Tip

Exam questions may expect you to remember about the existence of background radiation without mentioning it. Look out for count rates that do not drop to zero, or half-life graphs with a line that tends towards a value higher than zero.

When memorising lists of the causes of background radiation, make sure to choose at least one natural and one man-made cause as these are thought of quite separately.

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Katie M

Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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