Radioactivity is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation.

Background information:

  • Radioactivity was discovered by Henri Becquerel with photographic paper.
  • Pierre and Marie Curie discovered polonium and radium.
Radiation types:

alpha ( \alpha ), beta ( \beta ), gamma ( \gamma ).

Alpha particles

  • Groups of two protons and neutrons struck together ( _{2}^{4}\textrm{He} ).
  • They have a positive charge (+).
  • Have low penetrating power and are stopped by a sheet of paper.
  • General equation:_{A}^{Z}\textrm{x} \to _{Z-2}^{A-4}\textrm{(x-2)} + _{2}^{4}\textrm{He}-2 from atomic number, -4 from mass number, move two places back in the periodic table and add the alpha particle (_{2}^{4}\textrm{He}).

 Beta particles

  • Formed when neutron in unstable nucleus is changed into proton.
  • They have a negative charge (-).
  • More penetrative and are stopped by 5mm of aluminium.
  • General equation:_{A}^{Z}\textrm{x} \to _{Z+1}^{A}\textrm{(x+1)} + _{-1}^{0}\textrm{e}

Gamma rays

  • Has no mass or charge.
  • Only energy is emitted in waves of energy.
  • It has high penetrating power.
  • Can be stopped by thick lead.


Radioactive radiation is detected using Geiger-Müller tube.

Distinction between nuclear and chemical reactions

Nuclear Reactions

  • New element may be formed.
  • Change occur in nucleus.
  • No chemical bonds are broken or formed.

Chemical Reactions

  • No new element formed.
  • No change in nucleus.
  • Chemical bond-breaking and forming occurs.

The half-life of an element is the time taken for half of the nuclei in any given sample to decay.

Uses of radioisotopes:

  • Medical: Gamma radiation is used to kill cancer cells.
  • Archaeological: Used for carbon-dating.
  • Food irradiation: Gamma rays are used to kill disease-carrying organisms.
  • Industrial uses: To detect leaks in pipeline radioisotopes are added and detected using Geiger-Müller counter.
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