Background Radiation (SQA National 5 Physics): Revision Note

Background radiation

• Background radiation is defined as:

The radiation that exists around us all the time

• There are two types of background radiation:

  • Natural sources from radioactive elements that have always existed on Earth and in outer space

  • Man-made sources from human activity that adds to the amount of radiation humans are exposed to on Earth

• The count rate of detected levels of background radiation can vary significantly from place to place

Sources of background radiation

• The sources that make a significant contribution to background radiation include:

  • radon gas (in the air)

  • rocks and buildings

  • soil

  • food and drink

  • cosmic rays

Background radiation sources pie chart

Natural sources

• Rocks and buildings

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

  • Heavy radioactive elements, such as uranium and thorium, occur naturally in rocks in the ground

  • Uranium decays into radon gas

• Radon gas (in the air)

  • Radon gas is an alpha emitter

  • Radon gas is particularly dangerous if it is inhaled into the lungs in large quantities

  • The gas is tasteless, colourless and odourless, but it is not generally a health issue unless levels are significantly high

• 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

• 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

  • Therefore, soil, made from decomposed organic matter is also a source of background radiation

Man-made sources

• Medical sources

  • In medicine, radiation is used frequently

  • 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 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 and render areas devastated for centuries