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

  • radon gas (in the air)
  • rocks and buildings
  • food and drink
  • cosmic rays
• Sources of background radiation

  A) radon gas

  B) rocks and building materials

  C) medical

  D) x-rays

  E) food

  F) cosmic rays

  G) other

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

  • Radon gas
  • Rocks and buildings
  • Food and drink
  • Cosmic rays
• Ionising nuclear radiation can be measured using a detector connected to a counter
• The detector uses count rate measured in counts/s or counts/minute

  • The count rate is the number of decays per second
• The count rate decreases the further the detector is from the source

  • This is because the radiation becomes more spread out the further away it is from the source
• The Geiger-Müller tube is the most common device used to measure and detect the count rate of radiation

  • Each time it absorbs radiation, it transmits an electrical pulse to a counting machine
  • This makes a clicking sound and it displays the count rate on a screen
• The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Müller tube is absorbing

  • Therefore, it matters how close the tube is to the radiation source
  • The further away from the source, the lower the count rate detected
• Geiger–Müller tube detects count rate

  
• Examples of other radiation detectors include:

  • Photographic film (often used in badges)
  • Ionisation chambers
  • Scintillation counters
  • Spark counters
• If asked to name a device for detecting radiation, the Geiger-Müller tube is a good example to give

  • You can also refer to it as a GM tube, a GM detector, GM counter, Geiger counter etc. (The examiners will allow some level of misspelling, providing it is readable)
  • Don’t, however, refer to it as a ‘radiation detector’ as this is too vague and may simply restate what was asked for in the question
  • It is important to regulate the exposure of humans to radiation. The amount of radiation received by a person is called the dose
• Measurements of background radiation are used to determine a corrected count rate

  • This can be done by taking readings with no radioactive source present and then subtracting this from readings with the source present