The Random Nature of Decay (Edexcel GCSE Physics: Combined Science)

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The Random Nature of Decay

  • It cannot be predicted when a particular unstable nucleus will decay
  • 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 certain nucleus decaying in a given time period

  • This is done by the half-life which enables the activity of a very large number of nuclei to be predicted during the decay process
    • During one half-life a particular nucleus will have a 50% chance of decaying
    • This means that, on average, 50% of nuclei will decay during one half-life
    • As a result, the number of nuclei remaining after each successive half-life will on average halve
    • However, even after a large number of half-lives, there is still a small probability that a particular nucleus will not have decayed
    • As a result, the number of nuclei remaining will never quite fall to zero

  • 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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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.