AQA GCSE Physics

Revision Notes

4.2.7 Random Nature of Radioactive Decay

Random Nature of Radioactive Decay

  • It cannot be predicted when a particular unstable nucleus will decay
  • This is because radioactive decay is a random process, this means that:
    • There is an equal probability of any nucleus decaying
    • It cannot be known which particular nucleus will decay next
    • It cannot be known at what time a particular nucleus will decay
    • The rate of decay is unaffected by the surrounding conditions
    • It is only possible to estimate the probability of a nuclei decaying in a given time period
  • For example, a researcher might take some readings of background radiation
  • If the researcher reset the counter to zero, waited one minute and then took the count
    reading and repeated the procedure, they might obtain results such as:

32    11    25    16    28

  • The readings don’t appear to follow a particular trend
    • This happens because of the randomness of radioactive decay

Dice Analogy

  • An analogy is a way of understanding an idea by using a different but similar situation
  • Rolling dice is a good analogy of radioactive decay because it is similar to the random nature of radioactive decay

Dice, downloadable IGCSE & GCSE Physics revision notes

A dice roll is a random process because you don’t know when you will roll a particular value. However, you can determine the probability of a particular result

  • Imagine someone rolling a dice and trying to get a ‘6’
  • Each time they roll, they do not know what the result will be
  • But they know there is a 1/6 probability that it will be a 6
  • If they were to roll the dice 1000 times, it would be very likely that they would roll a 6 at least once
  • 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

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