Background Radiation (Cambridge O Level Physics)

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Background Radiation

  • Background radiation is the radiation that is always present around us in the environment

A Pie Chart Showing Sources of Background Radiation

background-radiation, IGCSE & GCSE Physics revision notes

Background radiation is the radiation that is present all around in the environment

  • Although most background radiation is natural, a small amount of it comes from artificial sources, such as medical procedures (including X-rays)
  • Levels of background radiation can vary significantly from place to place
    • Radiation from Nuclear Power come to less than 0.1% of the total

 

Sources of Background Radiation

  • Background radiation can come from natural sources on Earth or from space as well as man-made sources

Natural Sources

  • Radon gas (in the air)
    • Airborne radon comes from the ground
    • This is from the natural decay of uranium in rocks and soil
    • The gas is tasteless, colourless and oderless but it not generally a health issue 

  • Rocks and Buildings
    • 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
    • Natural radioactivity can be found in building materials, including decorative rocks, stone and brick

  • 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 utilised all the time
    • Uses include 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 would increase 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 and render areas devastated for centuries

Examiner Tip

The sources that make the most significant contribution are the natural sources:

  • Radon gas
  • Rocks and buildings
  • Food and drink
  • Cosmic rays

Make sure you remember these for your exam!

Accounting for Background Radiation

  • 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

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 notesDetermine the background radiation count.

 

Answer:

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 is moved back far enough it is all absorbed by the air before reaching the Geiger-counter
    • Results after 1 metre do 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

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Ann H

Author: Ann H

Expertise: Physics

Ann obtained her Maths and Physics degree from the University of Bath before completing her PGCE in Science and Maths teaching. She spent ten years teaching Maths and Physics to wonderful students from all around the world whilst living in China, Ethiopia and Nepal. Now based in beautiful Devon she is thrilled to be creating awesome Physics resources to make Physics more accessible and understandable for all students no matter their schooling or background.