Background Radiation (Cambridge (CIE) O Level Physics): Revision Note

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 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

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