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 Separate Physics and Combined Science

Atomic structure

This lesson builds nuclear equations, half-life and radiation safety for GCSE Physics.

Use the core lesson first, then match the exam-board guidance to your school route. Many pupils meet this content through Combined Science as well as Separate Physics.

Good forSeparate Physics and Combined Science
FocusNuclear equations, half-life and radiation safety
Time45-60 minutes
EquipmentCalculator, periodic table and half-life graph practice.
Paper fitPaper 1 focus on most GCSE Physics routes
TierFoundation core with Higher stretch
Practical linkNo required practical 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.

Exam-board fit

RouteSeparate Physics and Combined Science
PaperPaper 1 focus on most GCSE Physics routes
TierFoundation core with Higher stretch
Specification fitAtomic structure: Nuclear equations, half-life and radiation safety
Practical linkNo required practical focus
Maths ladderM1 substitution with units, M7 standard form and significant figures

Exact paper labels and specification-point numbering vary by board and cohort, so match this lesson to your school route before using past-paper questions.

Nuclear data supplied on this page

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

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.

Exam practice ladder

AO1 fluencyRecall the key definition, unit, equation or model before using the lesson questions.
AO2 applicationApply nuclear equations, half-life and radiation safety to an unfamiliar device, practical setup or data description.
AO3 analysisUse 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.

Exam-board guidance

All supported routes assess the core physics idea, but they may group topics, practicals and paper wording differently.

AQA GCSE Physics

AQA GCSE Physics: use this lesson for nuclear equations, half-life and radiation safety, then check whether your class is taking Separate Physics or Combined Science.

OCR GCSE Physics

OCR GCSE Physics: the core physics idea is shared, but Gateway and Twenty First Century may organise questions differently.

Pearson Edexcel GCSE Physics

Pearson Edexcel GCSE Physics: practise the concept, the equation use and the practical language because questions often connect them.

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: check whether your class is using the current GCSE Physics route or a newer science route, then use this lesson for the shared physics idea.

CCEA GCSE Physics

CCEA GCSE Physics: connect the idea to your unit and remember that practical skills are assessed directly.

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.

Next lesson

Next, continue with Motors and the Motor Effect.

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