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

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

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.

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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