Atomic structure
This lesson builds atomic structure, nuclear radiation and half-life 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.
What you will learn
Exam-board fit
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.
Decay data supplied on this page
Use the source, detector and half-life prompts to practise radiation type, penetration and decay calculations.
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
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.
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.
Exam practice ladder
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.
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 atomic structure, nuclear radiation and half-life, 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
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.
Next lesson
Next, continue with Magnetism and Electromagnetism.