Alpha, Beta & Gamma Radiation
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
Nuclear notation for an alpha particle (a helium nucleus)
- Alpha is the most ionising type of radiation
- This is due to it having the highest charge of +2e
- This means it produces the greatest number of ion pairs per mm in air
- This also means it is able to do more damage to cells than the other types of radiation
- Alpha is the least penetrating type of radiation
- This means it travels the shortest distance in air before being absorbed
- Alpha particles have a range of around 3-7 cm in air
- Alpha can be stopped by a single piece of paper
Beta Particles
- Beta (β−) particles are high energy electrons emitted from the nucleus
- Beta (β+) particles are high energy positrons (antimatter of electrons) also emitted from the nucleus
- β− particles are emitted by nuclei that have too many neutrons
- β+ particles are emitted by nuclei that have too many protons
Nuclear notation for beta minus and beta plus particle
- 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 Radiation
- Gamma (γ) rays are high energy electromagnetic waves
- They are emitted by nuclei that need to lose some energy
Nuclear notation for gamma rays
- If any of these types of radiation 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
- Gamma is the least ionising type of radiation
- This is because it is an electromagnetic wave with no charge
- This means it produces the least number of ion pairs per mm in air
- It can still cause damage to cells, but not as much as alpha or beta radiation. This is why it is used for cancer radiotherapy
- Gamma is the most penetrating type of radiation
- This means it travels the furthest distance in air before being absorbed
- Gamma radiation has an infinite range and follows an inverse square law
- Gamma can be stopped by several metres of concrete or several centimetres of lead
Different types of radiation are stopped by different materials
Comparing Alpha, Beta & Gamma
- The properties of the different types of radiation are summarised in the table below:
Comparing Different Types of Radiation Table
Worked example
ANSWER: D