CIE A Level Physics (9702) 2019-2021

Revision Notes

28.2.1 The Random Nature of Radioactive Decay

The Random Nature of Radioactive Decay

  • Radioactive decay is defined as:

The spontaneous disintegration of a nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle

  • The random nature of radioactive decay can be demonstrated by observing the count rate of a Geiger-Muller (GM) tube
    • When a GM tube is placed near a radioactive source, the counts are found to be irregular and cannot be predicted
    • Each count represents a decay of an unstable nucleus
    • These fluctuations in count rate on the GM tube provide evidence for the randomness of radioactive decay

Radioactivity Fluctuations, downloadable AS & A Level Physics revision notes

The variation of count rate over time of a sample radioactive gas. The fluctuations show the randomness of radioactive decay

Characteristics of Radioactive Decay

  • Radioactive decay is both spontaneous and random
  • A spontaneous process is defined as:

A process which cannot be influenced by environmental factors

  • This means radioactive decay cannot be affected by environmental factors such as:
    • Temperature
    • Pressure
    • Chemical conditions


  • A random process is defined as:

A process in which the exact time of decay of a nucleus cannot be predicted

  • Instead, the nucleus has a constant probability, ie. the same chance, of decaying in a given time
  • Therefore, with large numbers of nuclei it is possible to statistically predict the behaviour of the entire group

Exam Tip

Make sure you can define what constitutes a radioactive decay, a random process and a spontaneous decay – these are all very common exam questions!

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