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
Examiner Tip
If asked to name a device for detecting radiation, the Geiger-Müller tube is a good example to giveYou 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.
