O Level Physics Notes: Alpha, Beta and Gamma Radiation
The three main types of nuclear radiation are alpha, beta and gamma radiation. Their properties are summarised in the following table.
|
Type |
Mass in units of atomic mass units |
Charge |
Description |
|
Alpha |
4 |
2 |
Consists of 2 protons particles and 2 neutrons |
|
Beta |
0 |
-1 |
A fast moving electron |
|
Gamma |
0 |
0 |
High energy electromagnetic radiation |
All nuclear radiation originates from the nucleus. When the nucleus undergoes decay, it may emit one of these types of radiation which generally result in a more stable nucleus. A nucleus may undergo several decays before it becomes completely stable.
Properties
Alpha radiation is the least penetrating. In a cloud chamber, it leaves a dense, heavy track. It may be stopped by a piece of paper of a few cm of air. Because it is charged it will curve in an electric or magnetic field. It is the most dangerous if ingesting since all the radiation will then be absorbed by the body.
Beta radiation is more penetrating. Being lighter than an alpha particle, it leaves a less visible, longer track. It may be stopped by a few cm of aluminium. Because it is charged it will curve in an electric or magnetic field, and being oppositely charged to an alpha particle, it will curve the opposite way. It is less energetic and more penetrating than alpha radiation so less dangerous if ingested since more will escape from the body.
Gamma radiation is very penetrating. It can only be stopped by several cm of lead. It leave a very wispy track in a cloud chamber, and is not charged, so does not curve in an electric field. Most will escape from the body if ingested so this is the least dangerous form of radiation.
Uses
Alpha radiation is used in fire alarms. If smoke enters the detector, the amount of radiation leaving the sensor will fall significantly and the alarm will be triggered.
Beta radiation is used to control the thickness of sheet metal. If the metal is too thick the amount of radiation reaching the sensor will be reduced and the rollers will make the metal thinner via a feedback mechanism.
Gamma radiation is used in cancer treatment. It preferentially kills rapidly dividing cancer cells over healthy cells. Doses over several weeks may reduce the size of tumours significantly in this way.