The atom
A positive nucleus of protons and neutrons is surrounded by electrons. Most of the atom is empty space. Atomic number is protons; mass number is protons + neutrons. Isotopes have the same proton number but different neutron numbers.
Radioactivity
- Alpha: helium nucleus, highly ionising, poorly penetrating, stopped by paper.
- Beta: fast electron, moderately ionising, stopped by aluminium.
- Gamma: electromagnetic radiation, weakly ionising, reduced by thick lead or concrete.
Half-life is the time for the count rate or unstable nuclei to fall by half. Irradiation is exposure to radiation; contamination is unwanted radioactive material on or in an object. Nuclear fission splits a large nucleus; fusion joins small nuclei and powers stars.
Download Atomic structure slides (PowerPoint)
Taught with support from Joseph Danso, Science Lecturer in London. Book a session.