Background Radiation (Edexcel International A Level Physics)

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 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

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