This module covers the fundamental principles of radioactivity and nuclear physics. You will learn about atomic structure, types of ionising radiation, nuclear decay processes, half-life calculations, and the practical uses and dangers of radioactive materials.
Work through each section in order. Interactive simulations help you visualise key concepts. Complete the Knowledge Check at the end to test your understanding.
An atom consists of a tiny, dense nucleus containing protons (positive charge) and neutrons (no charge), surrounded by orbiting electrons (negative charge) arranged in shells.
The atomic number (Z) is the number of protons and defines the element. The mass number (A) is the total number of protons and neutrons (nucleons). Isotopes are atoms of the same element (same Z) with different numbers of neutrons (different A).
2 protons + 2 neutrons (helium nucleus). Highly ionising, low penetrating power. Stopped by paper or skin. Range: ~5 cm in air.
High-speed electron emitted when a neutron converts to a proton. Moderately ionising. Stopped by a few mm of aluminium. Range: ~30 cm in air.
Electromagnetic wave with no mass or charge. Weakly ionising but highly penetrating. Reduced by several cm of lead or metres of concrete.
Uncharged particle from nucleus. Penetrating; best absorbed by hydrogen-rich materials (water, concrete). Emitted in fission.
Example: 23892U → 23490Th + 42He
Example: 146C → 147N + 0−1e
No change in Z or A. The nucleus loses energy by emitting a gamma photon.
Photographic Film: Radiation darkens photographic film. Film badges are worn by workers to monitor exposure over time. The degree of darkening indicates the dose received.
Geiger-Müller (GM) Detector: A sealed tube filled with low-pressure gas. Radiation ionises the gas, causing a brief pulse of current that is counted electronically. Connected to a counter or ratemeter, it gives readings in counts per second or minute.
Background radiation is the low-level ionising radiation that exists naturally in the environment. It comes from both natural and artificial sources and must be accounted for in experiments.
Activity is the rate at which a radioactive source decays, measured in becquerels (Bq). 1 Bq = 1 decay per second.
The half-life is the time taken for the number of radioactive nuclei (or activity) to halve. It is constant for a given isotope and cannot be changed by physical or chemical means.
Half-lives passed: 0 | Remaining: 300/300
Beta radiation is used to monitor the thickness of paper, aluminium foil, or plastic during manufacturing. If the material becomes too thick, less radiation reaches the detector, and the rollers are adjusted automatically.
A gamma-emitting tracer is added to fluid flowing through underground pipes. Above ground, a detector scans along the pipe. A higher reading indicates a leak where the tracer escapes into the surrounding soil.
An alpha source ionises the air between two electrodes, allowing a small current to flow. When smoke enters, it absorbs the alpha particles, reducing ionisation and current. The drop in current triggers the alarm.
Irradiation: Exposure to radiation from an external source. The person or object does not become radioactive. Exposure stops when the source is removed.
Contamination: Radioactive material is deposited on or inside a person or object. The contaminated item continues to be exposed until the material is removed or decays. This is generally more dangerous as it is harder to control.
A hospital patient receives a targeted beam of gamma rays for cancer treatment.
Safety Precautions:
Radioactive Waste Disposal: Low-level waste (clothing, tools) is sealed and buried in shallow landfills. High-level waste (spent fuel rods) must be stored securely for thousands of years in deep geological repositories, as it remains dangerous for a very long time.
Test your understanding with these 10 questions. Select the best answer for each.