Radioactivity (radioactive decay)

• Radioactivity results from the spontaneous breakdown (decay) of atoms (isotopes) with unstable nuclei. These unstable isotopes are called radio isotopes.
• Radioactive decays are described as nuclear reactions because they involve nuclei in the centre of atoms. (In contrast, chemical reactions involve electrons in the outer parts of atoms.)

Alpha, beta and gamma radiation
There are three kinds of radiation emitted during radioactive decays.

• Alpha particles
• Beta particles
• Gamma rays
  
  
  
• Nuclear decay equations can be used to summarise radioactive decay processes. These decay equations must balance with respect to mass numbers and atomic numbers.
  
  

Background radiation
We are all exposed to background radiation. It is normally very low and causes no risk to our health.
Background radiation comes from:

• some rocks in the Earth, especially granite;
• bricks and other building materials;
• our food;
• the Sun which emits gamma rays.

Half-life

• Half-life is the time it takes for the activity, or the amount of a radioactiveisotope, to fall by half.
• The shorter the half life, the faster the isotope decays and the more unstable it is.