Alpha, Beta & Gamma Radiation (Edexcel A Level Physics): Revision Note

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 particles are the most ionising type of radiation

  • This is due to having the highest charge of +2e

  • They produce the highest number of ion pairs per cm in air (~10 000 ion pairs per cm)

  • This means they can do more damage to cells than the other types of radiation

• Alpha particles are the least penetrating type of radiation

  • This means they travel the shortest distance in air before being absorbed

  • They have a range of around 3 to 7 cm in air

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

• 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

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

• 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