Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want radioactivity — alpha, beta, gamma, half-life and safety — to become a reliable source of marks instead of a mix of penetration and equations.
What query it owns: how to understand and revise radioactivity in Cambridge IGCSE Coordinated Science.
Why this is safe: this page owns the radioactivity revision-guide angle, while Tutopiya’s Radioactivity subtopic page owns the learning resource and the free Radioactivity quiz owns the practice.

Radioactivity is the spontaneous emission of radiation from unstable nuclei. Cambridge IGCSE Coordinated Science (0654) expects you to compare alpha, beta and gamma radiation, interpret half-life graphs, and describe detection and safety precautions. This guide links each radiation type to the explanation and calculation questions examiners set.

Key takeaways

• Alpha (α): helium nucleus (²He), +2 charge, stopped by paper, highly ionising.
• Beta (β): high-speed electron, −1 charge, stopped by thin aluminium, moderate ionisation.
• Gamma (γ): electromagnetic wave, no charge, reduced by thick lead, weakly ionising.
• Half-life: time for half the nuclei (or activity) to decay — random process.
• Background radiation comes from natural and artificial sources; use shielding and distance for safety.

What is radioactivity in Cambridge IGCSE Coordinated Science?

Unstable isotopes decay by emitting ionising radiation — alpha, beta or gamma — until a stable nucleus forms. Each type differs in charge, mass, ionising power and penetration. Half-life measures how quickly activity falls: after one half-life, half the original radioactive nuclei remain. Geiger counters detect radiation; safety measures include limiting time, increasing distance and using shielding.

You can read the full explanation, diagrams and notes on Tutopiya’s Radioactivity subtopic page before you attempt questions.

Alpha, beta and gamma compared

Radiation	Nature	Charge	Stopped by	Ionising power	Penetration
Alpha (α)	²He nucleus	+2	Paper/skin	Strongest	Weakest
Beta (β)	Electron	−1	Thin Al sheet	Moderate	Moderate
Gamma (γ)	EM wave	0	Thick lead/concrete	Weakest	Strongest

Half-life calculations

Starting amount	After 1 half-life	After 2 half-lives	After 3 half-lives
800 counts/min	400	200	100
64 g	32 g	16 g	8 g

Example: half-life 6 hours, initial activity 1200 Bq → after 12 hours (2 half-lives): 1200 ÷ 4 = 300 Bq.

Radioactivity in past-paper wording

Command word	What the question wants	Typical stem
Compare	Properties of radiations	”Compare alpha and beta radiation.”
Calculate	Half-life from data	”Calculate the half-life from the graph.”
Explain	Safety or detection	”Explain why alpha sources must not be ingested.”
State	Penetration or nature	”State what stops beta radiation.”

Worked exam-style stems

1. “A radioactive source has a count rate of 640 counts/min. After two half-lives, what is the count rate?” After 1 half-life: 320; after 2: 160 counts/min. Reward: 160 with unit.
2. “Compare the penetrating power of alpha and gamma radiation.” Alpha is stopped by paper; gamma needs thick lead — gamma penetrates much further. Reward: correct stopping materials + gamma more penetrating.
3. “Explain why radioactive sources are stored in lead-lined containers.” Lead absorbs/shields ionising radiation, reducing exposure to people nearby. Reward: shielding + reduced dose.

Test yourself with the Radioactivity quiz once you can compare radiations and work through half-life steps.

How radioactivity connects to the syllabus

Radioactivity builds on The Nuclear Atom — unstable nuclei have excess energy. Medical and industrial uses appear in exam contexts. The Cambridge IGCSE Coordinated Science resource hub links every Atomic Physics subtopic.

Common mistakes students make

• Saying half-life is the time for radiation to stop completely (only half decays each half-life).
• Reversing penetration order (alpha least penetrating, gamma most).
• Stating beta is a proton (it is a high-speed electron).
• Forgetting background radiation when measuring count rates.
• Confusing activity (decays per second) with mass of source remaining.

When you need more support

If radioactivity comparison and half-life questions keep costing marks, work through the Radioactivity quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

Is radioactivity hard in Coordinated Science? Learn the three radiation types, half-life halving rule, and two safety measures — that covers most questions.

What is half-life? The time taken for half the radioactive nuclei in a sample to decay, or for activity to halve.

Which radiation is most penetrating? Gamma radiation — it requires thick lead or concrete to absorb it significantly.

How do I revise radioactivity effectively? Practise comparison tables, half-life calculations, safety explanations, then take the quiz.

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