Atomic and Nuclear Physics: notes

The atom

• Nucleus: protons (positive) and neutrons (no charge) at the centre.
• Electrons: negative, orbiting the nucleus. A neutral atom has equal protons and electrons.
• Proton number: the number of protons. Nucleon number: protons plus neutrons.
• Isotopes: atoms of one element with the same protons but different neutrons.

Radioactivity

• Alpha (α): a helium nucleus. Strongly ionising, stopped by paper.
• Beta (β): a fast electron. Stopped by a few millimetres of aluminium.
• Gamma (γ): electromagnetic wave. Weakly ionising, reduced by thick lead.
• Half-life: the time for half the radioactive nuclei to decay. After 3 half-lives, 1/8 remain.
• Detection: a Geiger-Müller tube counts radiation. Background radiation is always present.

Uses and safety

• Uses: medical tracers, sterilising equipment, checking thickness, dating old objects.
• Safety: keep sources in lead, handle with tongs and limit exposure time.
• Nuclear energy: fission splits a heavy nucleus; fusion joins light nuclei.