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
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
Worked example
ANSWER: D
Examiner Tip
It is important to be familiar the properties of each type of radiation and their symbols.