Learn about the different types of radiation

This lesson includes:

  • two videos
  • one activity


What is radiation?

Some elements have nuclei that are unstable.

Radiation is the process by which the nuclei decays in order to become stable again.

There are three types of radioactive decay:

  • alpha particle
  • beta particle
  • gamma ray

They are all examples of ionizing radiation.

This means they have enough energy to ionize (strip away electrons) other atoms they come into contact with.

Watch this short film where Jon Chase discusses the different types of radiation as well as observing alpha radiation first-hand.

Alpha (α) particle decay

Alpha particles are emitted when the unstable atom has too few neutrons.

They are the same as a helium nucleus, so they contain two protons and two neutrons.

Alpha particles:

  • have high ionizing power
  • cannot penetrate further than the thickness of skin/paper
Alpha particles can be represented using either of these ways.

Beta particle (β) decay

Beta particles are emitted when the nucleus has too many neutrons.

A neutron will turn into a proton and emit a fast-moving electron called a β particle.

They have no mass and have a negative charge.

Beta particles:

  • have low ionizing power
  • penetrate skin/paper but are stopped by around 3 mm of aluminium
Beta particles can be represented using either of these ways.

Gamma ray (γ) decay

After emitting an alpha or beta particle, the nucleus will often still be too ‘hot’ and will lose energy in a similar way to how a hot gas cools down.

It does this by releasing a gamma ray.

Gamma ray emission causes no change in the number of particles in the nucleus meaning both the atomic number and mass number remain the same.

Gamma rays:

  • have very low ionizing power
  • are very good at penetrating materials but are absorbed by lead/concrete

Detecting radiation

Radiation can be detected using a Geiger counter.

The radiations ionise the gas inside and the resulting charged particles move across the chamber and get counted as charges rather like an ammeter.

Watch this short film where Dr Kevin Fong demonstrates how to use a radiation detector.


Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve.

The half-life can also be the time it takes for the count rate to halve.

Count-rate is the number of decays recorded each second by a detector, such as the Geiger counter.

How a radioactive sample decays over time.

For example

The half-life of radioactive carbon-14 is 5,730 years.

If a sample of a tree (for example) contains 64 grams (g) of radioactive carbon, after 5,730 years it will contain 32 g, after another 5,730 years that will have halved again to 16 g.


There are lots of ways to try out your science skills.


Test what you know about radiation with this quiz.

There's more to learn

Have a look at these other resources around the BBC and the web.

GCSE Physics
BBC Teach - GCSE Physics
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