The three types of ionising radiation are: alpha, beta and gamma.

    1.  Alpha radiation

        The unstable nucleus of a radioactive element gives out alpha radiation.

        Alpha ...

• is a particle (Higher tier only: Alpha is identical to helium nucleus: 2 protons & 2 neutrons).

• is stopped by paper or few centimetres of air.

• The element that is left behind is a different element and more stable. It has 2 protons and
  
   two neutrons less that the original radioactive element.

    2. Beta radiation

        The unstable nucleus of a radioactive element gives out beta.

        Beta ...

• is a particle (Higher tier only: Beta is a high energy electron).

• penetrates paper.

• is stopped by few mm of aluminium.

• The element that is left behind is a different element and more stable. It has one more 
  
  proton than the original radioactive element.

    3. Gamma radiation

        An unstable nucleus gives out gamma radiation.

        Gamma ...

• is a high energy electromagnetic wave.

• penetrates paper.

• penetrates aluminium.

• is absorbed by few metres of concrete.

• is absorbed by few cm of lead