What is nuclear radiation?

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When atoms split (through fission or radioactive decay) or fuse together to make a bigger atom (fusion) energy is released, which is usually in the forms of

  • Alpha particles [1]: these comprise 2 neutrons and 2 protons, which is the same as a Helium nucleus,
  • Beta particles [2]: an electron or its anti-matter equivalent, the positron
  • Gamma rays [3]: electromagnetic radiation[4], like X-rays, ultra-violet, visible and infra-red light, microwaves and radio waves, having the highest energies of all these.

These are all ionising - able to break the bonds between atoms in molecules - which can damage DNA and destroy cells or start cancers in living organisms.

Alpha particles carry most energy but are most easily stopped - e.g. by human skin - although if they are emitted by radioactive isotopes which have got into the body they can seriously damage cells.

Beta particles have lower energy than alphas but can penetrate further.

Gamma rays carry least energy but have the highest penetrating power, and can require thick lead or concrete shielding to stop them.

Neutrons are also emitted by various fission and fusion processes. Neutrons are not ionising but when they hit other atoms they may transmute them into other isotopes which may be radioactive. Thus, some non-radioactive materials, when exposed to bombardment by neutrons in nuclear reactors or elsewhere, can be "activated" and become radioactive.