GCSE · Physics · Edexcel · Spec 1PH0

Background radiation

You're exposed to radiation right now — from the ground, from the sky, and even from your lunch.

Where does it come from?

From space down to the rock under your feet

A slice from space down into the ground — not to scale. Tap each layer to see where its background radiation comes from, and whether the level there is higher or lower.

↑ Space

↓ The rock beneath your feet

Zone 1 of 5

Space — an astronaut

This is where cosmic rays come from. The Sun and other stars give out high-energy radiation because of nuclear reactions taking place inside them, and some of it reaches Earth's atmosphere. An astronaut is exposed to even more cosmic rays than an airline pilot.

  • Source: the Sun and other stars
  • Astronaut: even more than a pilot

Radiation comes up from the ground and down from space. So the level where you are depends on two things: the rock underneath you (a lot of igneous rock usually means more) and how high you are (higher up means more exposure to cosmic rays).

Watch out: Keep the two reasons apart: igneous rock raises the radiation coming UP from the ground; height raises your exposure to cosmic rays coming DOWN from space.

Predict, then check

Picture an ordinary room: no hospital, no power station, nothing labelled radioactive.

A Geiger counter makes a click for each bit of radiation it detects. You switch one on in an ordinary room with no radioactive source nearby. What happens?

Radiation on your plate

?

Reason it through

How do radioactive atoms end up inside your own body?

Link 1 of 4

First link · your turn

Start underground. What is in the soil and rocks?

2
Locked — reveal the link above first
3
Locked — reveal the link above first
4
Locked — reveal the link above first

Natural or artificial?

Sort the sources

For each source, tick every box that is true. Then check your grid.

Rocks, and the radon gas some give off
Cosmic rays
Food
Carbon-14 in the air
Medical X-rays and radiotherapy
Nuclear weapons testing, nuclear power waste and research sources

Medical radiation, measured against background

Lowest-dose X-ray examinationsvsHigher-dose medical procedures

Background radiation makes a handy ruler: how many days or years of it would give the same dose?

Focus

Dose, compared with natural background radiation

Lowest-dose X-ray examinations

Similar to just a few days of natural background radiation

Higher-dose medical procedures

Equivalent to a few years of natural background radiation

The insight

Natural background radiation is the yardstick because it is the radiation we are all exposed to all of the time anyway.

Which dose is bigger?

Lowest-dose X-ray examinations

The smaller — days' worth

Higher-dose medical procedures

The bigger — years' worth

Natural or artificial?

Lowest-dose X-ray examinations

Artificial — a medical procedure

Higher-dose medical procedures

Artificial — a medical procedure

What do you really think?

Is radiation really everywhere?

Your friend reckons: 'Radiation's only a thing if you live next to a nuclear power station or work in a hospital X-ray department.'

Which idea is closest to what you think now?
How sure are you?

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

The radiation that is around us all the time — where it comes from, and why there is more in some places than others.

What you need to know

  • Background radiation is caused by unstable nuclei around us all the time — there is some just about everywhere.
  • Most sources are natural: rocks and radon gas, cosmic rays from space, food, and carbon-14 in the air.
  • Artificial sources include medical X-rays and radiotherapy, nuclear weapons testing, nuclear power waste and sources used in research.
  • The level is usually higher where there is a lot of igneous rock, and higher at greater heights because there is more exposure to cosmic rays.

The big picture

Background radiation is radiation from unstable nuclei that are around us all the time, so there is some just about everywhere. Most of its sources are natural — rocks and radon gas in the ground, cosmic rays from the Sun and other stars, the food we eat and the air we breathe — although some are artificial, such as medical X-rays and nuclear power waste. Its level changes from place to place: it is usually higher where there is a lot of igneous rock, and higher the higher up you go.

Key points

1Radiation here means tiny particles or high-energy electromagnetic waves given out by unstable atoms; substances that give it out are radioactive substances.
2Igneous rocks, formed from volcanic activity, often contain more radioactive atoms than other types of rock.
3Cosmic rays come from the Sun and other stars, where nuclear reactions give out high-energy radiation.
4Plants absorb minerals containing radioactive atoms through their roots, so food — and our bodies — contain some radioactive atoms.
5A Geiger counter clicks once for each bit of radiation it detects, so it still clicks now and then with no radioactive source nearby.
6The lowest-dose X-ray examinations give a dose similar to a few days of natural background radiation; higher-dose procedures, a few years.

Worked example

Problem

Explain why an airline pilot is exposed to a higher level of background radiation at work than a teacher working in a school at ground level.

⚠ Watch out

Thinking background radiation is mostly man-made. Most sources are natural — rocks and radon, cosmic rays, food and the air — and artificial sources such as X-rays and nuclear power waste are only some of them.

🧠

Memory hook

Up from the Rocks, down from the Stars, in through what you Eat and Breathe. Where you stand (igneous rock?) and how high you are (more cosmic rays?) decide how much you get.

✓

Check yourself

Without looking back: name one natural source that reaches you from below your feet, one that arrives from above, one that gets inside you — and one artificial source.

Flashcards

(14)
In this topic, what is 'radiation'?
Tiny particles or high-energy electromagnetic waves given out by unstable atoms.
What is a radioactive substance?
A substance that gives out this invisible radiation.
What causes background radiation, and where is it found?
Unstable nuclei that are around us all the time — so there is some background radiation just about everywhere.
Are most sources of background radiation natural or artificial?
Most are natural, although some are artificial.
Why is background radiation usually higher where there is a lot of igneous rock?
Igneous rock (formed from volcanic activity) often contains more radioactive atoms than other types of rock.
What is radon?
A radioactive gas that can come up from certain types of rock in the ground.
Cosmic rays: natural or artificial — and from which direction do they reach us?
Natural. They arrive from outer space, reaching the Earth from above.
Name a place on Earth's surface where background radiation is usually higher just because of height.
The top of a mountain.
Who is exposed to more cosmic rays: an airline pilot or an astronaut?
The astronaut. Pilots are exposed to higher levels than people on the ground, and astronauts to even more.
How do radioactive atoms get into your body through food?
Some minerals in soil and rocks contain radioactive atoms; plants absorb them through their roots; we eat the plants.
What is carbon-14, and how does it get into us?
A naturally occurring radioactive isotope of carbon found in the air — we breathe it in.
Name four artificial sources of radiation.
Medical procedures (X-rays and radiotherapy), nuclear weapons testing, nuclear power waste, and sources used in research.
What does a Geiger counter do?
It makes a click for each bit of radiation it detects and records the total.
How do medical imaging doses compare with natural background radiation?
The lowest-dose X-ray examinations: similar to a few days of natural background. Higher-dose procedures: equivalent to a few years.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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