2.5.6Forces, Space and Radioactivity

Sources of Background Radiation — WJEC GCSE Science (Double Award) - Physics Revision Notes & Topical Questions

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Part 1 of 4What background radiation is

Always present

Always present Background radiation is the low level of ionising radiation that is around us all the time, wherever we are.
It must be measured and subtracted from readings when you investigate a radioactive source.

Two types of source

Type	Description
Two types of source	Natural sources come from the environment and space.
Artificial	sources are produced by human activities.

Radon gas

Radon gas Rocks and soils contain tiny amounts of radioactive elements such as uranium, which decays into radon gas, an alpha emitter.
Radon seeps from the ground and building materials.
- It is dangerous if large amounts are breathed into the lungs, and levels are higher in areas such as Cornwall and parts of Wales.

Cosmic rays

Cosmic rays High-energy particles, mainly protons, arrive from the Sun, supernovae and other energetic events in space.
When they collide with molecules in the atmosphere they produce secondary radiation, including gamma rays.

Carbon-14 in living things

Carbon-14 in living things All plants and animals contain a very small amount of radioactive carbon-14,
- which is constantly replaced while they are alive.

Food and drink

Food and drink Food and water pick up radioactive elements from soil and rock.
- Bananas, for example, contain potassium-40.
The amounts are tiny and are not a health concern.

Source	Description	Contribution
Nuclear medicine	X-rays, CT scans, radioactive tracers and radiotherapy	The largest artificial source for most people
Nuclear waste	Used radioactive material from power stations, hospitals and industry	Small to the general public but dangerous to those handling it
Nuclear fallout	Radioactive dust thrown into the air by nuclear weapons tests or explosions	Very low now, but higher near test sites
Nuclear accidents	Events such as Chernobyl release large amounts of radioactive material	Rare, but can contaminate areas for centuries

1Natural sources dominate

Natural sources dominate For most people, natural sources provide most of the background radiation they receive.

2Radon is the biggest

Radon is the biggest Radon gas from rocks and buildings is usually the largest single contribution.

3Then food and cosmic rays

Then food and cosmic rays Radioactive material in food and drink and cosmic rays are the next most significant natural sources.

4Artificial sources are smaller

Artificial sources are smaller Medical uses are the main artificial source,
- while fallout, waste and accidents are normally very small for the average person.

Term	Meaning
Background radiation	The ionising radiation that is present in the environment all the time.
Radon	A radioactive gas formed by the decay of uranium in rocks, which emits alpha radiation.
Cosmic rays	High-energy particles from space that strike the Earth's atmosphere.
Nuclear fallout	Radioactive material that settles from the air after a nuclear explosion.
Artificial source	A source of radiation made or released by human activity.

Thinking background radiation comes mainly from nuclear power stations. Natural sources, especially radon, are far larger.

Saying radon can be seen or smelled. It is colourless, tasteless and odourless, and is detected using instruments.

Forgetting that background radiation is present in every measurement and must be subtracted from count rates.

Stating that cosmic rays are produced by the Earth. They come from the Sun and from events elsewhere in space.

Last updated: 20 October 2026