Detecting Radiation (Edexcel GCSE Physics): Revision Note

Detecting Radiation

• It is important to regulate the exposure of humans to radiation

• The amount of radiation received by a person is called the dose and is measured in sieverts (Sv)

• One sievert is a very big dose of radiation

  • It would cause acute radiation poisoning

• People would normally receive about 3 mSv (0.003 Sv) in one year

• To protect against over-exposure, the dose received by different activities is measured

• Radiation can be measured and detected using a photographic film or a Geiger–Müller tube

Photographic Film

• Photographic films detect radiation by becoming darker when it absorbs radiation, just like it does when it absorbs visible light

  • The more radiation the film absorbs, the darker it is when it is developed

• People who work with radiation, such as radiographers, wear film badges which are checked regularly to monitor the levels of radiation absorbed

• To get an accurate measure of the dose received, the badge contains different materials that the radiation must penetrate to reach the film

  • These materials may include aluminium, copper, paper, lead and plastic

• The diagram shows what a typical radiation badge looks like:

A badge containing photographic film can be used to monitor a person’s exposure to radiation

• The badge shows the amount of different types of radiation that the radiographer has been exposed to

• Different areas of the film are exposed to different types of radiation

  • Alpha radiation is unlikely to be detected at all as it will be absorbed / stopped by the paper

  • Beta radiation is absorbed by the aluminium

  • Gamma (or X-rays) affect all areas of the film but the lead will reduce some of the gamma radiation

Geiger-Müller tube

• The Geiger-Müller tube is the most common device used to measure and detect radiation

• Each time it absorbs radiation, it transmits an electrical pulse to a counting machine

• This makes a clicking sound or displays the count rate

• 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

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