Three types of ionising radiation are:
Alpha particle - is a helium nucleus, two protons and two neutrons. It has a large mass, compared to other ionising radiations, and a strong positive charge.
Beta particle - is a fast moving electron. It has a very small mass and a negative charge.
Gamma ray - is a high-energy electromagnetic wave. Gamma rays are caused by changes within the nucleus. They are part of the electromagnetic spectrum and so travel at the speed of light. They have no mass and no charge.
Each type of radiation has a different ability to penetrate materials. The material is said to have absorbed the radiation.
The energy of the three radiations is absorbed by the material through which the radiation passes. The amount of energy which is absorbed depends on the type of radiation and the type of the absorbing material.
|Radiation||Range (cm)||Ionising power||Can pass through paper?||Can pass through 5mm of aluminium||Can pass through 5cm of lead?||Electrical field deflection|
|Alpha||3-5||Highly ionising||No||No||No||Deflected towards negative plate|
|Beta||about 15||Ionising||Yes||No||No||Deflected towards positive plate|
|Gamma||much longer||Weakly ionising||Yes||Yes||No - although some will still get through||None|
Each type of radiation is caused by a decay (either spontaneous - natural - or induced - a reaction has caused the decay).
The nuclei of some atoms are unstable, and will naturally undergo 'radioactive decay'. This causes the release of ionising radiation which allows the nucleus to become more stable.
Atoms that do this are said to be radioactive.