S4.11.4 For the adult
Background radiation
A radiation counter reads some counts every minute, often 15 to 30, with no source anywhere near it. Where do they come from?
What this chapter teaches
Radiation is always around us. Most of it is natural: radon gas from rocks, gamma rays from rocks and soil, cosmic rays from space, and potassium 40 and carbon 14 in food and in our own bodies. The largest human source is medical. How much a person receives depends on the rock beneath, the height and the building. Dose is measured in sieverts, and the figures here are rounded world averages.
Three questions to ask
There is no one right wording. Listen for the idea.
- Which two natural sources of background radiation and one made by people can you name?
- Why can two houses in the same street have a different radon level?
- Why do people on a mountain top receive more cosmic rays?
After the chapter, the learner can
- Name natural sources of background radiation and ones made by people
- Explain why background radiation differs from place to place
What they copy into their notebook
Background radiation is always there. Natural: radon (about half), rocks, cosmic rays, food. Made by people: mostly medical. It varies with rock, height and buildings. Dose is in sieverts: 1 mSv = 1 000 µSv.