GCSE Physics · Edexcel 1PH0 · Topic 6B
Types of radiation and nuclear decay
Key points
- Alpha (α): a helium nucleus (2 protons, 2 neutrons). Highly ionising, stopped by paper or a few cm of air.
- Beta minus (β⁻): a fast electron from a neutron turning into a proton. Moderately ionising, stopped by a few mm of aluminium. Beta plus (β⁺) is a positron.
- Gamma (γ): high-frequency EM radiation. Weakly ionising, reduced by thick lead or concrete.
- In alpha decay mass number falls by 4 and atomic number by 2; in β⁻ decay mass number stays the same and atomic number rises by 1. Gamma emission changes neither.
- Decay is random: you cannot predict when a nucleus will decay. Background radiation comes from rocks, cosmic rays, food and medical sources.
- Radiation is detected with photographic film or a Geiger–Müller tube; subtract background from counts.
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Unstable nuclei become more stable by emitting radiation. This sub-topic compares the types of radiation, shows how to write balanced nuclear equations and explains where the background radiation around us comes from.
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