Alpha, Beta & Gamma Radiation (Edexcel International A Level Physics)

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Alpha, Beta & Gamma Particles

  • Some elements have nuclei that are unstable
    • This tends to be when the number of nucleons does not balance

  • In order to become more stable, they emit particles and/or electromagnetic radiation
    • These nuclei are said to be radioactive

  • There are three different types of radioactive emission: Alpha, Beta and Gamma

Alpha Particles

  • Alpha (α) particles are high energy particles made up of 2 protons and 2 neutrons (the same as a helium nucleus)
  • They are usually emitted from nuclei that are too large

Alpha particle, downloadable AS & A Level Physics revision notes


Beta Particles

  • Beta (β) particles are high energy electrons emitted from the nucleus
    • β particles are emitted by nuclei that have too many neutrons


  • Beta is a moderately ionising type of radiation
    • This is due to it having a charge of +1e
    • This means it is able to do some slight damage to cells (less than alpha but more than gamma)

  • Beta is a moderately penetrating type of radiation
    • Beta particles have a range of around 20 cm - 3 m in air, depending on their energy

  • Beta can be stopped by a few millimetres of aluminium foil


Gamma Rays

  • Gamma (γ) rays are high energy electromagnetic waves
  • They are emitted by nuclei that need to lose some energy

Gamma particle, downloadable AS & A Level Physics revision notes 

  • If these particles hit other atoms, they can knock out electrons, ionising the atom
  • This can cause chemical changes in materials and can damage or kill living cells

Ionisation, downloadable AS & A Level Physics revision notes

When radiation passes close to atoms, it can knock out electrons, ionising the atom

  • The properties of the different types of radiation are summarised in the table below

Table properties of alpha, beta, gamma radiation, downloadable AS & A Level Physics revision notes

  • u is the atomic mass unit (see “Atomic Mass Unit (u)”)
  • e is the charge of the electron: 1.60 × 10-19 C
  • c is the speed of light: 3 × 108 m s-1

Worked example


Worked example - alpha beta gamma particles (2), downloadable AS & A Level Physics revision notes

Exam Tip

It is important to be familiar the properties of each type of radiation and their symbols.

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Katie M

Author: Katie M

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

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