Describe the origins of background radiation from Earth and space

The idea

Background radiation is the low-level ionising radiation that is always present around us. Its origins fall into two groups. From Earth come radioactive substances in rocks and soil, notably isotopes of uranium and potassium, plus radon gas that seeps from the ground and can collect indoors; food and drink also carry small amounts of naturally radioactive atoms. From space come cosmic rays, high-energy particles from the Sun and beyond, which are strongest at high altitude and near the poles. Human-made sources such as medical X-rays add a little. A good answer names at least one Earth source and one space source and does not claim background radiation comes from a single origin.

What earns the marks

• Names an Earth origin such as radioactive rocks, soil, radon gas or naturally radioactive food and drink.
• Names a space origin such as cosmic rays arriving from the Sun or from beyond the Solar System.
• Distinguishes Earth-based sources from space-based sources rather than listing them as one group.
• Recognises that background radiation is present at a low level everywhere and is not caused by a single source.

Common mistakes and how to put them right

• Confuses background radiation with radiation from a nearby radioactive sample.

  Put it right: Keep the two ideas separate.

• Treats cosmic rays as coming only from the ground.

  Put it right: Link them to space and high altitude.

• Assumes all background radiation is human-made.

  Put it right: Include natural Earth and space sources.

Exam tips

• Learn one clear Earth example and one clear space example so you can name both quickly.
• Use the words 'Earth' and 'space' in your answer to show you have covered both parts of the statement.
• Remember radon gas as a common Earth source that can build up indoors.