The Random Nature of Radioactive Decay (Cambridge International A-Level Physics)

Spec point — 23.2.1

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 the decay of an unstable nucleus
  • These fluctuations in count rate on the GM tube provide evidence for the randomness of radioactive decay

Graph of radioactive decay

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, i.e. 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 Hint Make sure you can define what constitutes a radioactive decay, a random process and a spontaneous decay - these are all very common exam questions!