GCSE Physics · AQA 8463 · Topic 4.4.2
Atoms and nuclear radiation
Key points
- Radioactive decay is random: you cannot predict which nucleus will decay next. Activity is the decay rate in becquerels (Bq); a Geiger–Muller tube measures the count-rate.
- Alpha (2 protons + 2 neutrons): very ionising, stopped by paper, range a few cm in air.
- Beta (fast electron from the nucleus): moderately ionising, stopped by a few mm of aluminium.
- Gamma (electromagnetic wave): weakly ionising, needs thick lead or concrete to reduce it.
- In equations, alpha decay lowers mass number by 4 and atomic number by 2; beta decay keeps the mass number but raises the atomic number by 1; gamma changes neither.
- Half-life is the time for the number of unstable nuclei, or the count-rate, to halve.
- Irradiation is exposure to radiation from outside; contamination is when radioactive atoms get onto or into something.
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Some nuclei are unstable and become more stable by giving out radiation. This sub-topic covers the four types of nuclear radiation, how to write the decays as equations, and how half-life describes the way a radioactive source gets weaker…
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