Background Radiation (AQA GCSE Physics)
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
What is Background Radiation?
Background radiation is defined as:
The radiation that exists around us all the time
Sources of Background Radiation
There are two types of background radiation:
Natural sources
Man-made sources
Background radiation is the radiation that is present all around in 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
Man-made sources of radiation increase the background radiation levels, examples include:
Fallout from nuclear weapons testing and nuclear accidents
Exposure from medical testing
Worked Example
A student is using 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 here.
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
Examiner Tips and Tricks
Students sometimes confuse background radiation with cosmic microwave background radiation (CMBR). Background radiation and CMBR do sound similar, but they are not the same thing. Although cosmic rays are also a contributing factor of background radiation.
Background radiation is the constant low-level radiation we are all exposed to on Earth every day. Radiation is released from the decay of tiny amounts of radioactive substances (like uranium) in the rocks below ground; these tiny amounts of radioactive substances can end up in our food and water as well.
Cosmic rays are particles that travel from the Sun or nearby stars and are mainly protons or small nuclei. Cosmic rays interact with the Earth's atmosphere, sending showers of smaller particles down toward the Earth's surface, providing a constant, low-level source of radiation.
Cosmic Microwave Background Radiation is radiation from the Big Bang explosion that is still travelling outwards across the Universe. CMBR is an EM wave that has been stretched out over time to the microwave region of the EM spectrum.
Cosmic rays and CMBR are beyond the scope of AQA GCSE Physics, but by learning just a little about each, you can see that background radiation and CMBR are completely different phenomena.
Measuring Radiation Dose
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
A dosemeter measures the amount of radiation in particular areas
A dosemeter, or radiation badge, can be worn by a person working with radiation in order to keep track of the amount of radiation they are receiving
Differences in Exposure
The level of background radiation and radiation dose may be affected by a person’s occupation or location
Some areas around the world have higher background radiation because they are closer to sources of radiation
People that work with nuclear radiation receive more radiation
The UK limit for nuclear industry employees is 20 mSv in one year
The diagram below compares the dose received by some different activities
All living things emit a small amount of radiation: the amount of radiation within a banana is tiny, and not at all dangerous!
Examiner Tips and Tricks
You have been introduced to three different units to do with radiation:
Becquerels measure the amount of radiation emitted by a source every second
Counts per second measures the rate at which radiation hits a particular location
Sieverts measure the received dose of radiation
They are not the same thing!
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