Overview
What you’ll learn
- Compare alpha, beta and gamma radiation in penetration, ionisation and range.
- Write nuclear equations for alpha and beta decay that balance.
- Define activity in Bq and read half-lives from decay graphs.
- Calculate what remains after any number of half-lives.
- Distinguish contamination from irradiation, and correct for background.
- Evaluate uses — tracers, radiotherapy, sterilisation, dating — against hazards.
Specification checklist (AQA 8463 · Edexcel 1PH0 · OCR Gateway J249)
Statements are paraphrased from the shared DfE subject content and grouped by tier. Foundation content is studied by every student; Higher statements are examined on Higher-tier papers only, and statements badged Physics only are examined in separate (triple) Physics, not Combined Science. QuizQuip is not affiliated with AQA, Pearson Edexcel or OCR.
Foundation — every student
- 7.1Describe that some atomic nuclei are unstable and may emit radiation (alpha, beta, gamma) as they change to become stable; this is a random process called nuclear radiation.
- 7.2Describe alpha particles (helium nuclei, 2 protons + 2 neutrons), beta particles (fast electrons ejected when a neutron changes into a proton) and gamma rays (electromagnetic waves), including their penetrating and ionising powers and ranges.
- 7.3Write balanced nuclear equations for alpha and beta decay, and recall that the emission of a neutron changes neither charge nor chemical identity.
- 7.4Define the activity of a radioactive source in becquerels (Bq), as the number of decays per second, and describe how it is measured with a Geiger–Müller detector as a count rate.
- 7.5Define half-life as the time for the number of unstable nuclei (or the activity) to halve, and calculate activities or amounts remaining after a whole number of half-lives.
- 7.6Interpret decay graphs (activity or count rate against time) to read off half-life and to predict how long activity takes to fall to a given level, and explain why decay cannot be predicted for a single nucleus.
- 7.7Describe background radiation from natural and man-made sources (radon, cosmic rays, rocks, medical, nuclear industry and fallout) and correct measurements for it.
- 7.8Distinguish radioactive contamination (unwanted radioactive atoms on or in an object) from irradiation (exposure to radiation), and describe their different hazards and precautions.
- 7.9Describe uses of nuclear radiation — medical tracers, radiotherapy, sterilising equipment, thickness control, smoke alarms and radiocarbon dating — and evaluate each choice of isotope and radiation.
- 7.10Describe the hazards of ionising radiation to living cells (tissue damage, mutation, cancer) and how the hazard depends on the type of radiation and the half-life, including the disposal of radioactive waste.
Key points
- 1Unstable nuclei emit radiation randomly and spontaneously — a nuclear process unaffected by temperature or chemistry.
- 2Alpha (α): helium nucleus (2p + 2n) · stopped by paper/skin · most ionising · range a few cm in air.
- 3Beta (β⁻): a fast electron from a neutron → proton change · stopped by a few mm of aluminium · moderately ionising.
- 4Gamma (γ): an electromagnetic wave · stopped by thick lead or concrete · least ionising · almost unlimited range in air.
- 5Nuclear equations balance mass numbers and atomic numbers on both sides; alpha decay drops A by 4 and Z by 2, beta decay raises Z by 1.
- 6Activity (becquerels, Bq) = decays per second; measured as a count rate with a Geiger–Müller tube (minus background).
- 7Half-life: the time for the activity (or nuclei count) to halve — after n half-lives, what remains is the start ÷ 2ⁿ.
- 8Contamination = radioactive atoms where you do not want them · irradiation = exposure to a source · hazards and precautions differ.
Notes · 1 of 5
Alpha, beta and gamma
Three radiations, one trade-off: the more ionising, the more easily stopped.
| Property | Alpha (α) | Beta (β⁻) | Gamma (γ) |
|---|---|---|---|
| Nature | Helium nucleus: 2 protons + 2 neutrons | Fast electron (from a neutron → proton change) | Electromagnetic wave |
| Relative charge | +2 | −1 | 0 |
| Penetration | Stopped by paper or skin | Stopped by a few mm of aluminium | Reduced by thick lead or concrete |
| Ionising power | Strongest | Moderate | Weakest |
| Range in air | A few centimetres | A few tens of centimetres to metres | Many metres, effectively unlimited |
| Deflected by fields? | Yes (both electric and magnetic) | Yes (opposite way to alpha) | No |
The inverse relationship is worth memorising: alpha rips through matter up close but cannot travel far; gamma travels far but rarely interacts. All three radiations are ionising — they knock electrons off atoms, which is precisely how they damage living cells and how detectors “see” them.
Notes · 2 of 5
Nuclear equations
Balance the top numbers and the bottom numbers — the nucleus keeps the accounts.
A nuclear equation tracks A (mass number) and Z (atomic number) through a decay. Alpha decay: A drops by 4, Z by 2 — radium-226 becomes radon-222 by emitting a helium nucleus: ²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂α. Beta-minus decay: a neutron turns into a proton, firing out an electron and an antineutrino; A is unchanged, Z rises by 1 — carbon-14 becomes nitrogen-14: ¹⁴₆C → ¹⁴₇N + ⁰₋₁β. Gamma emission changes neither A nor Z — the nucleus simply sheds energy. Neutron emission likewise leaves Z alone.
Notes · 3 of 5
Activity, count rate and half-life
Randomness en masse becomes a reliable exponential clock.
A single unstable nucleus decays randomly — no one can say when. But a sample of billions behaves predictably: its activity, the number of decays per second, measured in becquerels (Bq), falls by the same fraction in equal times. The half-life is the time for the activity (or the number of unstable nuclei) to halve. Detectors report a count rate — a sample of the decays — which you first correct by subtracting the background count. After n half-lives, what remains is the starting value ÷ 2ⁿ.
| Half-lives elapsed | Fraction remaining | Activity from 800 Bq |
|---|---|---|
| 0 | 1 | 800 Bq |
| 1 | 1/2 | 400 Bq |
| 2 | 1/4 | 200 Bq |
| 3 | 1/8 | 100 Bq |
| 4 | 1/16 | 50 Bq |
Notes · 4 of 5
Background radiation, contamination and irradiation
The world is already faintly radioactive — and there is a difference between being near it and wearing it.
Background radiation reaches every detector: radon gas from rocks (the largest natural share in UK homes), cosmic rays, radioactive rocks in the ground, and small man-made contributions (medical procedures, the nuclear industry, historic fallout). Good measurements subtract it: measured rate − background rate = corrected rate. Irradiation means being exposed to radiation from a source nearby — stop the exposure (distance, shielding, removing the source) and it ends. Contamination means radioactive atoms are on or inside you or the object — they keep irradiating until physically removed. Contamination is the worse hazard for workers: gloves, suits and careful disposal exist to prevent it.
| Property | Irradiation | Contamination |
|---|---|---|
| What it is | Exposure to radiation from an outside source | Radioactive atoms on or inside an object or body |
| Stops when | The source is removed or shielded | The atoms are removed (cleaning, excretion) |
| Main defence | Distance, shielding, time limits | Gloves, suits, containment, careful waste handling |
Notes · 5 of 5
Uses and hazards of radiation
The same ionising power that harms cells also traces, treats and sterilises.
- Medical tracers: a gamma- or beta-emitting isotope (e.g. technetium-99m, half-life 6 hours) is injected and followed through the body — gamma escapes for detection, and the short half-life limits the dose.
- Radiotherapy: focused gamma beams (from cobalt-60) kill cancer cells; the high dose damages healthy tissue too, so beams are rotated to spread the entry dose.
- Sterilisation: gamma rays kill bacteria on syringes and food without heating them.
- Thickness control (foil and paper mills): beta absorption measures thickness continuously.
- Smoke alarms: americium-241’s alpha radiation ionises air; smoke drops the current and the alarm sounds.
- Radiocarbon dating: carbon-14’s half-life (5 700 years) dates once-living material.
The hazards mirror the uses: ionising radiation damages or kills cells and can mutate DNA, causing cancer. Alpha sources are the most dangerous inside the body (all their ionising power lands in one place) but barely dangerous outside; gamma is the workplace external hazard. Half-life shapes the choice: tracers need short half-lives so the patient is not irradiated for long; dating and industrial gauges need long ones. Radioactive waste must be stored for many half-lives until its activity falls — one reason nuclear decommissioning is slow and costly.
Revise
Key terms
The words examiners expect you to use precisely.
- Radioactive decay
- The random, spontaneous emission of radiation from an unstable nucleus.
- Alpha particle
- A helium nucleus (2p + 2n), strongly ionising, stopped by paper.
- Beta particle
- A fast electron released when a neutron changes into a proton.
- Gamma ray
- An electromagnetic wave emitted by a nucleus shedding energy.
- Nuclear equation
- A balanced equation tracking mass number and atomic number through a decay.
- Activity
- The number of decays per second, measured in becquerels (Bq).
Show 6 more key termsShow fewer key terms
- Count rate
- The number of detections per second measured by a Geiger–Müller tube, corrected for background.
- Half-life
- The time for half the unstable nuclei in a sample — or the activity — to decay.
- Background radiation
- The ever-present radiation from radon, cosmic rays, rocks and man-made sources.
- Irradiation
- Exposure to radiation from an external source.
- Contamination
- Radioactive atoms getting onto or into an object or body.
- Radiotherapy
- The controlled use of high-dose radiation to kill cancer cells.
Revise
Common mistakes
Where students most often lose marks in this chapter — and what to do instead.
Mistake: Saying you can predict when one nucleus will decay.
Decay is random for individual nuclei.
Instead: Only the behaviour of large samples is predictable — half the nuclei halve their count in one half-life, on average.
Mistake: Saying half-life is “half the time it takes to decay completely”.
The activity never reaches zero — it keeps halving.
Instead: Each half-life halves whatever remains: 100 → 50 → 25 → 12.5, forever approaching zero.
Show 10 more mistakesShow fewer mistakes
Mistake: Writing a beta decay equation with A changed.
A neutron became a proton — the total nucleons are unchanged.
Instead: Beta-minus: A stays, Z rises by 1, an electron (⁰₋₁β) is emitted.
Mistake: Putting the alpha particle’s charge as −2.
Alpha particles are helium nuclei — positive.
Instead: Alpha = 2 protons + 2 neutrons, charge +2.
Mistake: Saying gamma rays are the most ionising.
It is the least — but it travels furthest.
Instead: Ionising power runs alpha > beta > gamma; penetration runs the other way.
Mistake: Forgetting to subtract background from a count rate.
The detector clicks even with no source present.
Instead: Corrected rate = measured rate − background rate, before any half-life work.
Mistake: Using contamination and irradiation as synonyms.
One is atoms on you; the other is rays on you.
Instead: Contamination = unwanted radioactive atoms present; irradiation = exposure to radiation.
Mistake: Choosing a long-half-life isotope for a medical tracer.
The patient stays radioactive for months.
Instead: Tracers need short half-lives (hours) so the dose ends quickly.
Mistake: Saying alpha emitters outside the body are the most dangerous external hazard.
Alphas cannot even reach the living cells under skin.
Instead: Alpha is deadliest inside the body; gamma is the main external hazard.
Mistake: Reading the half-life from the time the graph reaches zero.
The graph never reaches zero.
Instead: Read the time for the activity to halve — 800 → 400, 400 → 200, and so on.
Mistake: Believing radioactivity can be sped up by heating.
Nuclear decay ignores temperature and chemistry.
Instead: Decay is spontaneous and nuclear — heating, freezing or reacting chemically changes nothing.
Mistake: Treating nuclear waste as safe after one half-life.
Half remains — and it is still hazardous.
Instead: Waste is stored for many half-lives until activity falls to safe levels.
Check yourself
Quick quiz
24 questions with instant explanations. About 5 minutes.
Question 1 of 3
- Question 1: current question
- Question 2: not answered
- Question 3: not answered
Identify radiations
The nucleus of a helium atom, ejected whole from a radioactive nucleus, is called
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Practise
Topical questions
12 exam-style questions with model answers and mark schemes.
A set of structured and calculation questions matched to this chapter, in three tiers, each with a model answer, mark scheme and examiner tip. Higher-tier and Physics-only questions are tagged.
Practise topical questionsExam practice
Practice paper
A 30-mark paper in the style of a GCSE paper, with a separate mark scheme. Give yourself 40 min.
Question paper
Chapter 7 Practice Paper
30 marks · 40 min · 5 pages
10 multiple-choice questions and structured questions with answer lines. Chapter 7: alpha, beta and gamma radiation, nuclear equations, activity and half-life, decay graphs, background radiation, contamination vs irradiation, uses and hazards.
Mark scheme
PROChapter 7 Practice Paper — mark scheme
Answers · Marking points · 3 pages
Model answers with a mark for each creditworthy point — for marking at home or in class.
How is this chapter examined?
Paper 1
1 h 45 · 100 marks
Chapters 1–7: energy, electricity, particle model, atomic structure
Paper 2
1 h 45 · 100 marks
Chapters 8–18: forces, waves, magnetism and electromagnetism, space physics
Tiers
Foundation (grades 1–5) · Higher (grades 4–9)
Higher assumes all Foundation content; the equation sheet is printed
Want a full paper? Try the Paper 1-style (Foundation), Paper 1-style (Higher), Paper 2-style (Foundation), Paper 2-style (Higher), Required practicals practice sets.
Questions
Frequently asked questions
How do I answer any half-life calculation?
Find the number of half-lives (time elapsed ÷ half-life), then divide the starting activity by 2ⁿ. Reverse questions ask the same thing backwards — count the halvings and multiply by the half-life.
Which radiation is which in a practical question?
Test each absorber in order: paper cuts the count (alpha), aluminium cuts it (beta), lead is needed (gamma). Always subtract the background first.
Why is an alpha emitter dangerous only inside the body?
Alpha cannot even penetrate skin, so outside it barely matters — but inside, its powerful ionisation lands entirely on a few cells. That is why alpha sources are sealed and never ingested.
What is the difference between a tracer and radiotherapy?
A tracer uses a tiny activity and a short half-life to image the body; radiotherapy uses a high, focused dose to kill cells. Same physics, opposite dose intent.
Is this chapter examined on both papers?
Atomic structure and radioactivity sit in AQA Paper 1 and in the first half of the Edexcel and OCR courses; they appear on Foundation and Higher papers of every board.
Does QuizQuip have any connection to the exam boards?
No. AQA, Pearson Edexcel and OCR are named only to identify the specifications this content supports. QuizQuip is not affiliated with, endorsed by, or connected to AQA, Pearson Edexcel or OCR, and no past-paper or specimen material is reproduced.
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Chapter 8: Forces and motion