Free GCSE Physics lesson: Nuclear Equations
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Free Lessons -> GCSE / Key Stage 4 -> Physics -> Nuclear Equations

Lesson 34 · GCSE / Key Stage 4 · Physics

Nuclear equations, half-life and safety

Balance nuclear equations, use half-life data and choose radiation safety controls.

Qualification: GCSE Subject: Physics Radioactivity

Atomic structure

Lesson overview

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

FocusNuclear equations, half-life and radiation safety
Time45-60 minutes
EquipmentCalculator, periodic table and half-life graph practice.
Practical linkNo separate practical method focus
Maths tagsM1 substitution with units, M7 standard form and significant figures

What you will learn

  • Balance mass number and atomic number in nuclear equations.
  • Describe alpha and beta decay using nuclear notation.
  • Use half-life from tables and graphs.
  • Select safety controls for radioactive sources.

Nuclear data supplied on this page

Use the isotope, decay and safety prompts to practise balancing nuclear changes and explaining source handling.

Nuclear equations, half-life and safety infographic

Infographic explaining GCSE Physics nuclear equations, half-life and safety, including alpha and beta minus decay, conservation of mass number and atomic number, half-life graph evidence, time, distance and shielding safety controls, and the difference between contamination and irradiation.
Use this visual to balance nuclear equations, read half-life evidence and explain radiation safety controls.Download visual

Clear explanation

In nuclear equations, the total mass number and total atomic number are conserved. This lets you work out a missing particle or daughter nucleus.

Alpha decay emits a helium nucleus, so mass number falls by 4 and atomic number falls by 2. Beta minus decay increases atomic number by 1 while mass number stays the same.

Radiation safety is about reducing exposure: limit time, increase distance, use shielding and avoid contamination.

Key graph

Activity halving over three half-lives A stepped half-life guide shows activity decreasing from nine hundred and sixty becquerels to four hundred and eighty, two hundred and forty and one hundred and twenty over three equal half-life intervals. number of half-lives activity / Bq 960 480 240 120
Graph: each equal time interval halves the activity, so pupils can count half-lives without ambiguity.

Worked examples

Alpha decay

A nucleus emits an alpha particle.

Mass number decreases by 4.

Atomic number decreases by 2.

Answer: If uranium-238 emits alpha radiation, the daughter nucleus has mass number 234 and atomic number 90.

Quick checks

Choose an answer, then check your thinking.

1. What happens to mass number in alpha decay?

2. Which safety action reduces radiation exposure by separation?

Practice questions

Question 1

An alpha decay starts with mass number 210 and atomic number 84. What are the daughter numbers?

Reveal answer and marking guidance

Answer: Mass number 206 and atomic number 82.

Marking: Credit subtracting 4 from mass number and 2 from atomic number.

Question 2

What happens to atomic number in beta minus decay?

Reveal answer and marking guidance

Answer: It increases by 1.

Marking: Credit neutron changing into proton with electron emitted.

Question 3

A source activity falls from 960 Bq to 120 Bq. How many half-lives have passed?

Reveal answer and marking guidance

Answer: Three half-lives.

Marking: Credit 960 -> 480 -> 240 -> 120.

Question 4

Give two ways to reduce exposure when handling a sealed source.

Reveal answer and marking guidance

Answer: Use tongs to increase distance and store it behind shielding.

Marking: Credit time, distance, shielding or contamination controls.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply nuclear equations, half-life and radiation safety 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

  • Not conserving atomic number in nuclear equations.
  • Confusing alpha particles with electrons.
  • Saying half-life depends on sample size.
  • Using shielding but ignoring contamination risk.

Extension challenge

Write and balance one alpha and one beta decay equation using isotope notation from your class notes.

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 nuclear equations, half-life and radiation safety.

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 Motors and the Motor Effect.

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