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Science

The electromagnetic spectrum

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Ionising radiation

Radioactive substances give out radiation all of the time. There are three types of nuclear radiation: alpha, beta and gamma. Alpha is the least penetrating, while gamma is the most penetrating. Nonetheless, all three are ionising radiation: they can knock electrons out of atoms and form charged particles.

Radiation can be harmful, but it can also be useful - the uses of radiation include to:

  • detect smoke
  • gauge the thickness of paper
  • treat cancer
  • sterilise medical equipment.

Types of radiation

Nuclear radiation comes from the nucleus of an atom. Substances that give out radiation are said to be radioactive. All radiation transfers energy. There are three types of nuclear radiation:

  • alpha
  • beta
  • gamma.

Radiation can be absorbed by substances in its path. For example, alpha radiation travels only a few centimetres in air, beta radiation travels tens of centimetres in air, while gamma radiation travels many metres. All types of radiation become less intense the further the distance from the radioactive material, as the particles or rays become more spread out.

The thicker the substance, the more radiation is absorbed. The three types of radiation penetrate materials in different ways.

alpha radiation cannot pass through humans, beta is stopped by aluminium, gamma by lead

Penetrative properties of different types of radiation

Alpha radiation

Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a sheet of paper.

Beta radiation

Beta radiation can penetrate air and paper. It can be stopped by a thin sheet of aluminium.

Gamma radiation

Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead or many metres of concrete.

Check your understanding by having a go at this animation. Click on each image of the rock to discover the reading on the radiation meter. Use the readings to confirm that the rock gives out beta radiation.

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