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Natural sources of background radiation are rocks and soil, including radon gas, and cosmic rays from space. Free GCSE Physics notes and 15 FAQs.
Sources of Background Radiation is part of Hazards and uses of radioactive emissions and of background radiation (physics only) in GCSE AQA Higher Physics.
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Natural sources of background radiation are rocks and soil, including radon gas, and cosmic rays from space. Free GCSE Physics notes and 15 FAQs.
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Use this lesson to stay inside Hazards and uses of radioactive emissions and of background radiation (physics only) while connecting the detail back to the wider Atomic structure topic.
Read the core explanations from Sources of Background Radiation before testing yourself from memory.
Right now, as you read this, invisible radiation is passing through your body. It comes from rocks beneath your feet, building materials around you, and outer space. At normal levels, background radiation presents a very low risk, but it still contributes to your lifetime radiation exposure.
Background radiation is like the hum of a busy city - always there, usually unnoticed, but measurable if you have the right equipment. A Geiger counter will click constantly, even in an 'empty' room, detecting this natural radioactivity.
Nature provides most of our background radiation through two main routes: from below (rocks and soil) and from above (cosmic rays). These sources have been active for billions of years, long before humans existed.
Cosmic rays are like a constant shower of invisible bullets from space. When they hit our atmosphere, they create cascades of secondary particles. Some of these reach ground level and contribute to background radiation. The atmosphere acts as a shield - that's why radiation levels are higher at altitude where there's less air protection.
The ground beneath you contains radioactive elements like uranium-238, thorium-232, and their decay products. Granite rocks are particularly radioactive because they contain more uranium. Radon gas, produced by uranium decay, seeps from rocks and soil into buildings.
While natural sources dominate background radiation, human activities have added their own contribution. These man-made sources are much smaller than natural ones, but they're worth understanding because they're the ones we can control.
Nuclear weapons testing, particularly atmospheric tests in the 1950s and 1960s, scattered radioactive material globally. The Chernobyl accident in 1986 and Fukushima in 2011 also released radioactive material, though most settled locally. These events created artificial isotopes like caesium-137 and strontium-90 that don't occur naturally.
Medical procedures using radioactive tracers, nuclear power generation, and even smoke detectors (which contain americium-241) contribute tiny amounts to background radiation. The key point is that man-made sources typically add less than 20% to the total background radiation level.
When measuring background radiation, you'll notice the count rate fluctuates randomly. This is because radioactive decay is a random process - you can't predict exactly when the next atom will decay. That's why we take readings over several minutes and calculate an average.
Background radiation isn't the same everywhere. A Geiger counter in Cornwall (granite bedrock) will click faster than one in East Anglia (sedimentary rocks). Understanding these variations helps explain why some areas have naturally higher radiation levels.
Worked example: Calculating Average Background Count Rate
A student measures these background counts: 28, 31, 25, 33, 28 counts in five separate 1-minute periods. Calculate the average count rate.
Answer: 0.48 counts per second (or 29 counts per minute)
Altitude affects background radiation because there's less atmosphere to absorb cosmic rays. Airline pilots and frequent flyers receive higher radiation doses than ground-based workers. Rock type matters too - granite contains more uranium than limestone, so areas like Scotland and Cornwall have higher natural background levels.
Exam questions on background radiation often test your understanding of sources and variation. The key is being specific about which sources are natural versus man-made, and explaining why levels vary geographically.
Common exam mistake: Students often forget that background radiation must be subtracted when measuring the activity of a radioactive source. If your Geiger counter shows 50 counts per second with a source present, and background is 5 counts per second, the source activity is 45 counts per second, not 50.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Radon gas is a radioactive gas produced by uranium decay, which seeps from rocks and soil into buildings. It is one of the natural sources of background radiation, along with rocks, soil and cosmic rays.
Background radiation is low-level ionising radiation that is present everywhere in the environment at all times. A Geiger counter clicks constantly even in an empty room because it detects this natural radioactivity, which presents a very low risk at normal levels.
Natural sources of background radiation are rocks and soil, including radon gas, and cosmic rays from space. Man-made sources include fallout from nuclear weapons testing and nuclear accidents such as Chernobyl, plus medical tracers, nuclear power and smoke detectors; man-made sources typically add less than 20%.
Cosmic rays are high-energy particles from outer space that constantly bombard Earth's atmosphere, creating secondary radiation that reaches the ground. The atmosphere acts as a shield, so radiation levels are higher at altitude, and airline pilots receive higher doses.
Man-made sources of background radiation include nuclear weapons testing, reactor accidents such as Chernobyl (1986) and Fukushima (2011), medical tracers, nuclear power generation and smoke detectors containing americium-241. They typically add less than 20% to the total.
Nuclear fallout is radioactive particles released into the atmosphere from nuclear weapons testing or reactor accidents, which eventually settle on the ground and contribute to background radiation. It created artificial isotopes like caesium-137 and strontium-90.
To measure background radiation, take Geiger counter readings over several periods and calculate an average, because the count rate fluctuates randomly. Readings of 28, 31, 25, 33 and 28 counts in five 1-minute periods give 145 ÷ 5 = 29 counts per minute.
Terrestrial radiation is radiation from naturally occurring radioactive elements in rocks, soil and building materials, particularly uranium, thorium and radon gas. Granite rocks are particularly radioactive because they contain more uranium.
Background radiation is higher in Cornwall because of its granite bedrock: granite contains more uranium than other rocks, and radon gas produced by uranium decay seeps from rocks and soil into buildings. Areas with sedimentary rocks, like East Anglia, have lower levels.
Background radiation is higher at altitude because there is less atmosphere to absorb cosmic rays. This is why airline pilots and frequent flyers receive higher radiation doses than ground-based workers.
The average background count rate is found by adding all the readings and dividing by the number of readings. Counts of 28, 31, 25, 33 and 28 in five 1-minute periods total 145, so the average is 145 ÷ 5 = 29 counts per minute, or 0.48 counts per second.
The background count rate fluctuates randomly because radioactive decay is a random process, so no one can predict exactly when the next atom will decay. Readings are therefore taken over several minutes and averaged.
Cornwall and Scotland have higher background radiation because their granite bedrock contains more uranium than limestone or the sedimentary rocks of East Anglia. A Geiger counter in Cornwall clicks faster than one in East Anglia.
A Geiger counter clicks constantly even in an 'empty' room because it detects background radiation, low-level ionising radiation that is present everywhere at all times. Its sources include rocks, building materials and outer space.
Natural sources provide most background radiation, from rocks and soil and from cosmic rays from space. Man-made sources typically add less than 20% to the total, but they are the ones humans can control.