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
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
The random nature of radioactive decay is such an important concept to grasp, yet in my experience of teaching this topic to GCSE students, it often gets forgotten after students are introduced to the maths. To firmly embed the concept of randomness in my student's minds, we would enact the decay of a radioactive sample.
Each student was given a dice and asked to stand up. The total number of students represented the number of nuclei in the sample. On my count, students would roll the dice. Those who rolled an odd number decayed, and sat down. Those who rolled an even number remained undecayed. Each roll of the dice represents one half-life. Because the probability of rolling an odd number is 50%, roughly half of the students would 'decay' with each passing half-life. By acting it out in this way, students really understood the random nature of the decay process and it gave us a model to refer back to throughout the topic that was tangible and memorable to them.
