Background Radiation (WJEC GCSE Science (Double Award)): Revision Note

Katie M

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Katie M

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Background Radiation

  • It is important to remember that radiation is a natural phenomenon

  • Radioactive elements have always existed on Earth and in outer space

  • However, human activity has added to the amount of radiation that humans are exposed to on Earth

  • Background radiation is defined as:

    The radiation that exists around us all the time

  • Every second of the day there is some radiation emanating from natural sources such as:

    • Rocks

    • Cosmic rays from space

    • Foods

Chart of Background Radiation Sources

Background Radiation Chart, downloadable AS & A Level Physics revision notes

Background radiation is the radiation that is present all around in the environment. Radon gas is given off from some types of rock

  • Although most background radiation is natural, a small amount of it comes from artificial sources, such as medical procedures (including X-rays) and nuclear power stations

  • The waste materials from these artificial sources are radioactive and some of them will remain radioactive for thousands of years

  • Consequently, this waste must be stored and disposed of carefully

Accounting for Background Radiation

  • 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

Measuring Background Count Rate

2-7-background-radiation-gm-tube-set-up-no-source

The background count rate can be measured using a Geiger-Müller (GM) tube with no source present

  • For example, if a Geiger counter records 24 counts in 1 minute when no source is present, the background radiation count rate would be:

    • 24 counts per minute (cpm)

    • 24/60 = 0.4 counts per second (cps)

Measuring Corrected Count Rate of a Source

2-7-background-radiation-gm-tube-set-up

The corrected count rate can be determined by measuring the count rate of a source and subtracting the background count rate

  • Then, if the Geiger counter records, for example, 285 counts in 1 minute when a source is present, the corrected count rate would be:

    • 285 − 24 = 261 counts per minute (cpm)

    • 261/60 = 4.35 counts per second (cps)

  • When measuring count rates, the accuracy of results can be improved by:

    • Repeating readings and taking averages

    • Taking readings over a long period of time

Worked Example

A student uses a Geiger counter to measure the counts per minute at different distances from a source of radiation. Their results and a graph of the results are shown below.

Background example, downloadable IGCSE & GCSE Physics revision notes

Determine the background radiation count.

Answer:

Step 1: Determine the point at which the source radiation stops being detected

  • The background radiation is the amount of radiation received all the time

  • When the source is moved back far enough it is all absorbed by the air before reaching the Geiger counter

  • Results after 1 metre do not change

  • Therefore, the amount after 1 metre is only due to background radiation

Step 2: State the background radiation count 

  • The background radiation count is 15 counts per minute

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.