Nucleus = protons and neutrons; electrons are in shells

Isotopes = same element with different mass number

Background radiation = many causes, some man-made

Alpha (highly ionising, low penetration), Beta (stopped by a few mm of foil), Gamma (high penetration > v dangerous)

Uses of radiation (Beta: quality assurance, Gamma: medical instruments & food freshness)

Nuclear fission = atom divides > releases neutrons

Chain reactions = result of released neutrons