Radioactivity · revision map · IGCSE 0625, Topic 5.2
TOPIC 5.2 · RADIOACTIVITY
CAMBRIDGE IGCSE PHYSICS 0625 · ONE-PAGE REVISION MAP
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RADIOACTIVITY5.2
Detection & Background
Unstable nuclei give out radiation at random. The moment a single nucleus decays cannot be predicted.
- Background radiation is always present.
- Sources: rocks and soil, cosmic rays, food, medical scans.
- A Geiger-Muller (GM) tube and counter detect and count it.
- Always subtract the background count from a reading.
Alpha, Beta & Gamma
Three kinds of nuclear radiation, with different charge and penetrating power:
- α alpha: a helium nucleus, charge +2, strongly ionising.
- β beta: a fast electron, charge −1, medium range.
- γ gamma: an EM wave, no charge, very penetrating.
Alpha stopped by paper; beta by a few mm of aluminium; gamma only reduced by thick lead.
Decay Equations
Decay changes one nucleus into another. Equations must balance A and Z on both sides.
- Alpha decay: A falls by 4, Z falls by 2.
- Beta decay: A unchanged, Z rises by 1 (a neutron becomes a proton, an electron is emitted).
Half-life
The half-life is the time for half the nuclei (or the activity) to decay.
- Each half-life halves what remains.
- Decay is random, but each isotope has a fixed half-life.
Safety & Uses
Staying safe
- Keep your distance and limit the time of exposure.
- Shield sources with lead and store them safely.
- Wear protective clothing; handle with tongs, not bare hands.
Everyday uses
- Smoke alarms use alpha.
- Medical tracers and sterilising equipment use gamma.
- Carbon dating and thickness gauges use beta.
- Radiotherapy treats cancer with gamma.