Key learning points

1. Background radiation is caused by unstable nuclei that are around us all of the time.
2. Atoms are very small with a radius of about 1 × 10⁻¹⁰ m.
3. The alpha particle scattering experiment (Rutherford, 1909) provides evidence for the size and nature of atomic nuclei.
4. An atomic nucleus has a radius about 10 000 times smaller than that of an atom.
5. Most of the mass of an atom is in its nucleus.

Keywords

• Background radiation - the radiation in the surroundings of a particular place

• Alpha particle - a small, positively charged particle which was used to discover the nucleus

• Alpha scattering experiment - the experiment used to discover the atomic nucleus from the deflection of alpha particles fired at it

• Nucleus - the central part of an atom which contains most of the mass and all of the positive charge

Common misconception