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