Free GCSE Physics lesson: Radioactivity
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Lesson 7 · GCSE / Key Stage 4 · Physics

Atomic structure and radioactivity

Learn nuclear structure, alpha, beta and gamma radiation, half-life and safe handling ideas.

Qualification: GCSE Subject: Physics Atoms

Atomic structure

Lesson overview

This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.

FocusAtomic structure, nuclear radiation and half-life
Time45-60 minutes
EquipmentCalculator and half-life graph practice.
Practical linkNo separate practical method focus
Maths tagsM1 substitution with units, M6 ratio and percentage, M7 standard form and significant figures

What you will learn

  • Describe the nucleus in terms of protons and neutrons.
  • Compare alpha, beta and gamma radiation.
  • Use half-life to reason about radioactive decay.
  • Explain contamination, irradiation and basic safety controls.

Decay data supplied on this page

Use the source, detector and half-life prompts to practise radiation type, penetration and decay calculations.

Atomic structure and radiation infographic

Infographic explaining atomic structure and radiation, including nuclei, alpha, beta and gamma radiation, half-life and safety.
Use this visual to compare radiation types and link decay to half-life evidence.Download visual

Clear explanation

Atoms have a tiny nucleus containing protons and neutrons, with electrons around the outside. Radioactive decay happens when an unstable nucleus changes.

Alpha radiation is strongly ionising but weakly penetrating. Beta is moderately ionising and penetrating. Gamma is weakly ionising but very penetrating.

Half-life is the time taken for the activity or number of undecayed nuclei to halve. Decay is random for individual nuclei but predictable for large samples.

Key graph

Half-life decay graph A radioactive decay graph curves down from high activity to half, then a quarter, then an eighth over equal time intervals. time activity / Bq half the starting activity
Graph: activity falls by the same fraction over each half-life interval, producing a curve rather than a straight line.

Worked examples

Using half-life

A source has activity 800 Bq. Its half-life is 3 days.

After 3 days: 400 Bq.

After 6 days: 200 Bq.

Answer: After two half-lives, the activity is 200 Bq.

Quick checks

Choose an answer, then check your thinking.

1. Which type of nuclear radiation is stopped by paper or skin?

2. A sample falls from 320 Bq to 80 Bq in two half-lives. What is one half-life if this takes 10 days?

Practice questions

Question 1

A source has activity 640 Bq. Calculate the activity after three half-lives.

Reveal answer and marking guidance

Answer: 80 Bq.

Marking: Credit 640 -> 320 -> 160 -> 80 Bq.

Question 2

Which radiation is most penetrating: alpha, beta or gamma?

Reveal answer and marking guidance

Answer: Gamma.

Marking: Credit gamma, with shielding such as thick lead or concrete if explained.

Question 3

Explain the difference between irradiation and contamination.

Reveal answer and marking guidance

Answer: Irradiation is exposure to radiation; contamination is radioactive material getting onto or into an object or person.

Marking: Credit clear distinction between exposure and material being present.

Question 4

Why is radioactive decay described as random?

Reveal answer and marking guidance

Answer: You cannot predict exactly when one particular unstable nucleus will decay.

Marking: Credit unpredictability for individual nuclei while large samples have measurable half-life.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply atomic structure, nuclear radiation and half-life to an unfamiliar device, practical setup or data description.
Practical interpretationUse evidence, graph features, uncertainty, method quality or conclusion wording where the question asks you to evaluate.
Maths skillM1 substitution with units

Answers and marking guidance

The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.

Common mistakes

  • Saying half-life is the time for all radiation to disappear.
  • Confusing irradiation with contamination.
  • Thinking gamma is the most ionising because it is most penetrating.
  • Forgetting that decay changes the nucleus.

Extension challenge

Sketch a half-life curve for activity falling from 400 Bq to 50 Bq over three half-lives and label each halving.

Reveal answer

Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.

Exam-board guidance

Short board notes only. Learn the core physics above first.

AQA GCSE Physics

AQA GCSE Physics: often rewards clear physics explanations, correct equations, units and practical evidence for atomic structure, nuclear radiation and half-life.

OCR GCSE Physics

OCR GCSE Physics: often values precise definitions, clear working, graph interpretation and links between models and evidence.

Pearson Edexcel GCSE Physics

Pearson Edexcel GCSE Physics: often combines the concept with equation use, data handling and practical interpretation.

Eduqas GCSE Physics

Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.

WJEC Wales

WJEC Wales: often expects accurate terms, units and evidence-based explanations using the shared physics idea.

CCEA GCSE Physics

CCEA GCSE Physics: connect the idea to your current unit and use the same practical method language your class uses.

Next lesson

Next, continue with Magnetism and Electromagnetism.

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