Atoms and Radioactivity

Information about atoms and... radioactivity, condensed down into 5 revision cards.

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Electrons, Protons and Neutrons

Atoms are made up of 3 sub-atomic particles. The protons and neutrons are found in the nucleus of the atom and the electrons orbit the nucleus within electron shells.


         Proton                     2000                           +1

         Neutron                   2000                             0

         Electron                      1                              -1

The atom is neutrally charged as there are the same number of protons as there are electrons.

To find out how many protons or electrons are in an atom, you find out the atomic number of the element. To find out how many neutrons are in an atom, you subtract the atomic number of the element from the atomic mass number.

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Isotopes are atoms of the same element which have the same number of protons but a different number of neutrons.

Protons are held together by the strong nuclear force. It is strong enough to hold the nucleus together in spite of the protons' electric force repelling them from each other.

The presence of neutrons affects the balance between these forces so too many or too few neutrons make the nucleus unstable. Unstable nuclei eventually decay which gives out energy and possibly alpha or beta particles.

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Ionising Radiation

Unstable nuclei emit ionising radiation which causes atoms to gain or lose electric charge, forming ions.

Alpha Radiation:

  • Alpha particles are helium nuclei.
  • Relative charge of alpha particle is +2.
  • Alpha particles have a short range (a few cm).
  • Alpha particles cannot penetrate more than a few mm of paper.
  • Alpha particles have strong ionising power.

Beta Radiation:

  • Beta particles are fast moving electrons.
  • Relative charge of beta particle is -1.
  • Beta particles can travel through long distances through air.
  • Beta particles are absorbed by dense materials, like aluminium.
  • Beta particles have weaker ionising power than alpha particles .
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Ionising Radiation

Gamma Radiation:

  • Gamma rays are electromagnetic waves with very short wavelengths.
  • Gamma rays have no mass and no charge.
  • Gamma rays can travel virtually infinitely.
  • Gamma rays can be stopped by a thich lead sheet.
  • Gamma rays have weak ionising power.
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Nuclear Transformation

Alpha Decay:

222               218           4

Radium  -->   Radon  +  Helium  + energy

88                86             2

Beta Decay:

14               14              0

Carbon  -->  Nitrogen  + electron  + energy

6                 7               -1

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