Contents
Key Stage 4
Meaning
An alpha particle (α-particle) is a type of ionising radiation made of 2 protons and 2 neutrons emitted from the nucleus of an unstable isotope.
About Alpha Particles
- Alpha particles may also be referred to as alpha radiation and is written with the symbol α.
- Alpha particles are a Helium nucleus.
- Alpha particles have a relative atomic mass of 4 and relative charge of +2.
- Alpha particles are emitted when a nucleus is too large or the ratio of protons to neutrons is too large.
- Alpha particles are emitted rather than single protons or neutrons because the Helium nucleus is extremely stable.
Charge and Mass
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Scientist were able to determine the charge and mass of α-particle by sending it between two electrically charged plates and observing its path.
The α-particle moves towards the negative plate, so it must be positively charged. The rate of curvature depends on the mass:charge ratio which indicates it has a relative atomic mass of 4 and relative charge of +2. |
Penetration Depth
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Alpha particles can travel around 5cm through air (STP) before colliding with and ionising atoms or molecules. |
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Alpha particles can be stopped by a thin sheet of paper. |
Ionising Potential
- With a charge of +2, α-particles are the most ionising of the three ionising radiations. It is capable of removing two electrons from a single atom or molecule or removing 1 electron from two atoms or molecules.
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| When an α-particle interacts with an atom the α-particle can remove one or two electrons to ionise the atom. |
Precautions
- Alpha radiation is the most ionising but the least penetrating.
- Outside the body an organism can be protected from alpha radiation by keeping a distance greater than 5cm or by covering any bare skin.
- When handling a source of alpha radiation the precautions which should be taken are:
- Wear gloves
- Use tongs to handle the source, never touch it.
- Aim the source away from any living organism.
- Store the source in a sealed container.