Radioactive decay and nuclear radiation Radioactive decay and nuclear radiation


  • Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process called radioactive decay.

Activity is the rate at which a source of unstable nuclei decays. Activity is measured in becquerel (Bq)

Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube).

The nuclear radiation emitted may be:

  • an alpha particle (α) – this consists of two neutrons and two protons, it is the same as a helium nucleus
  • a beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton
  • a gamma ray (γ) – electromagnetic radiation from the nucleus
  • a neutron (n).
  • Required knowledge of the properties of alpha particles, beta particles and gamma rays is limited to their penetration through materials, their range in air and ionising power.
  • Students should be able to apply their knowledge to the uses of radiation and evaluate the best sources of radiation to use in a given situation.

WS 1.4 Explain everyday and technological applications of science; evaluate associated personal, social, economic and environmental implications; and make decisions based on the evaluation of evidence and arguments.

WS 1.5 -Evaluate risks both in practical science and the wider societal context, including perception of risk in relation to data and consequences.

MS 1b -Recognise and use expressions in standard form

MS 1c -Use ratios, fractions and percentages

MS 3c -Substitute numerical values into algebraic equations using appropriate units for physical quantities







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Changes in the nucleus


Changes in the nucleus ANS


Changes in the nucleus


Changes in the nucleus ANS