Module Overview

KLO 7.1 — Units: becquerel (Bq), centimetre (cm), hour (h), minute (min), second (s)

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.

Fundamentals of Radioactivity

Atomic Structure (KLO 7.2, 7.3)

KLO 7.2: Describe the structure of an atom (protons, neutrons, electrons).
KLO 7.3: Define atomic number (Z), mass number (A), and isotopes.

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).

Example: Carbon-14 (146C) has 6 protons, 8 neutrons, and 6 electrons. It is an isotope of Carbon-12 (126C), which has only 6 neutrons.

Simulation: Atom Builder

Element: Carbon  |  Symbol: 126C  |  Protons: 6  |  Neutrons: 6  |  Electrons: 6  | 

Types of Ionising Radiation (KLO 7.4, 7.5)

KLO 7.4: Describe alpha, beta, gamma radiation and neutron emission.
KLO 7.5: Compare ionising power and penetrating power of each type.

Alpha (α) — 42He

2 protons + 2 neutrons (helium nucleus). Highly ionising, low penetrating power. Stopped by paper or skin. Range: ~5 cm in air.

Beta (β−) — 0−1e

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.

Gamma (γ)

Electromagnetic wave with no mass or charge. Weakly ionising but highly penetrating. Reduced by several cm of lead or metres of concrete.

Neutron (n) — 10n

Uncharged particle from nucleus. Penetrating; best absorbed by hydrogen-rich materials (water, concrete). Emitted in fission.

Penetration Power

SRC Paper Aluminium Lead α STOPPED β STOPPED γ REDUCED

Simulation: Penetration Experiment Lab (KLO 7.6)

Count Rate: 0 counts/min

Nuclear Equations (KLO 7.7, 7.8)

KLO 7.7: Write balanced nuclear equations for alpha and beta decay.
KLO 7.8: Describe gamma emission and neutron emission.

Alpha Decay

AZX → A−4Z−2Y + 42He

Example: 23892U → 23490Th + 42He

Beta Decay (β−)

AZX → AZ+1Y + 0−1e

Example: 146C → 147N + 0−1e

Gamma Emission

AZX* → AZX + γ

No change in Z or A. The nucleus loses energy by emitting a gamma photon.

Neutron Emission

AZX → A−1ZY + 10n

Simulation: Nuclear Decay Animator

Simulation: Nuclear Equation Practice

Score: 0 / 0

Detection of Radiation (KLO 7.9)

KLO 7.9: Describe how radiation is detected.

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 (KLO 7.10)

KLO 7.10: Describe sources of background radiation.

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.

Click a segment to learn more about that source.

Radioactive Decay, Uses, and Dangers

Activity and Half-Life (KLO 7.11, 7.12)

KLO 7.11: Define activity and the becquerel.
KLO 7.12: Define half-life and describe how it relates to radioactive decay.

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.

Remaining = Initial ÷ 2n    where n = number of half-lives = time ÷ half-life

Half-Life Calculator (KLO 7.13)

KLO 7.13: Calculate activity or count rate after a given number of half-lives.

Half-Life Decay Visualizer

Half-lives passed: 0 | Remaining: 300/300

Simulation: Inverse Square Law

I = I0 / (3)2 = I0 / 9    Relative Intensity: 11.1%

Simulation: Geiger Counter

Count Rate: 0 Bq

Uses of Radioactivity (KLO 7.14)

KLO 7.14: Describe uses of radioactivity in medicine, industry, and agriculture.

Thickness Gauge (Beta Source)

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.

Paper/foil β β source DET Detector Signal to control system Roller Roller

Pipe Leak Detection (Gamma Tracer)

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.

Ground level Underground pipe γ tracer in fluid Leak GM Detector (high reading)

Smoke Detector (Alpha Source)

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.

Normalαα source+−+−+−IonsCurrent flowsWith SmokeαSmokeAlarm triggered!

Contamination vs Irradiation (KLO 7.15)

KLO 7.15: Distinguish between contamination and irradiation.

Irradiation: Exposure to radiation from an external source. The person or object does not become radioactive. Stops when the source is removed.

Contamination: Radioactive material is deposited on or inside a person or object. Contaminated item continues to be exposed until removed or decayed.

Scenario 1 of 6 Score: 0 / 0

A hospital patient receives a targeted beam of gamma rays for cancer treatment.

Dangers of Radioactivity (KLO 7.16)

KLO 7.16: Describe the dangers of ionising radiation and safety precautions.
Biological Effects: Ionising radiation can damage or destroy living cells. It can cause:
  • Cell death — high doses kill cells directly (radiation sickness)
  • Mutations — damage to DNA can cause cancer or be passed to offspring
  • Severity depends on dose, radiation type, and exposure time

Safety Precautions: Keep distance, minimise exposure time, use shielding (lead, concrete), handle with tongs, store in lead-lined containers, wear protective equipment and film badges.

Radioactive Waste Disposal: Low-level waste sealed and buried. High-level waste stored securely for thousands of years in deep geological repositories.

Knowledge Check

Test your understanding with these 10 questions. Select the best answer for each.