Gamma: more information

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Gamma rays () are electromagnetic waves, rather like X rays and radio waves.
Thus gamma rays have no mass and no charge.

You can find out more about electromagnetic waves from

After a nucleus has emitted an -particle or a -particle, it may still have too much energy: we say it is in an "excited state".

It can get rid of this energy by emitting a pulse of very high frequency electromagnetic radiation, called a gamma ray.

-particles and -particles pull electrons off atoms as they pass (we say the ionise the atoms), but rays don't. This means that they do not lose much energy as they travel, as they do not interact as much with the matter they pass.
Therefore, gamma rays have a high penetrating power, and a very long range.

It's worth noting that there is no such thing as a pure -ray source. Gamma rays are given off by most alpha emitters and beta emitters. If we want a source of pure gamma rays, we can get it by using a substance that emits both beta and gamma, and simply keep it in an aluminium container that stops the beta particles.

Useful gamma sources include Technetium-99, which is used as a "tracer" in medicine. This is a combined beta and gamma source, and is chosen because betas are less harmful to the patient than alphas (less ionisation) and because Technetium has a short half-life (just over 6 hours), so it decays away quickly and reduces the dose to the patient.


Remember, in Gamma decay:-

  • atomic number unchanged
  • atomic mass unchanged.


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