In terms of progressing through the material, the sequence below ensures that students starting from first principles will meet each item having the prerequisite knowledge. It is not a strict teaching order, as some items (for example, Rutherford scattering) can be taught in isolation and some depend only very lightly on previous material: for example, students don't need to know about the various types of radioactive decay in order to understand the exponential nature of decay.
- stability of the nucleus - the idea that some nuclei are unstable, and that they undergo radioactive decay (often in more than one step) to become stable
- nuclear changes in decay - the effect of alpha, beta and gamma decay on the number of protons and neutrons in the nucleus. For more able students, this could lead on to looking at balanced nuclear equations
- the range and penetrating power of alpha and beta particles and gamma rays
- the decay constant and exponential decay - the fact that radioactive decay is a random process (be extra aware of students' misconceptions of what random means!) and that this random process leads to exponential decay
- half-life - this follows on from the previous topic on exponential decay and involves working with the radioactive dice graphs produced
- fission and electricity generation - beginning with a brief look at the use of fission in electricity generation, and then moving on to a more detailed look at the fission process and the chain reaction
- fusion - this follows on from fission, and introduces students to the famous E=mc2 equation. It is important to stress that the equation means that mass and energy are equivalent - the same thing - rather than it being an equation in the mould of speed = distance / time or voltage = current × voltage
- Rutherford scattering - pupils do not need to know what an alpha particle is before they begin this, but the concept will be easier to explain if they do
Points to consider:
- the way that students use the word random is very different to its meaning within physics. To many students, random means unlikely or strange, so it's important to point out this difference to them.
- students should have learnt it during GCSE, but some always forget that half-life is the time taken for half of the remaining nuclei to decay - a sample isn't all gone after two half-lives
- the liquid drop model may be useful in explaining to the more inquisitve pupils why larger nuclei are more prone to decay
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.
Links and Resources
The important activity here is TAP 515-3, which uses dice to model radioactive decay. Students begin with a large number of dice (eg 50) and throw them all; they count the number that come up (eg 1), and remove these from the pile and then re-throw the remaining dice. They continue this process until there are no "un-decayed" dice remaining.
Plotting a graph of dice remaining against number of throws will yield an exponential decay curve. More able students can use Excel and it's curve-fitting trendline function to find the radioactive decay equation and therefore the time constant.
Analysis of exponential decay curves and the random decay of radioactive nuclei leads onto a discussion of half-life, which comes next.
This is a great fun video from the old Teachers' TV series Inside Science. It will be useful for teaching about the nuclear fission chain reaction.
The video looks at the mechanics of nuclear fission and the chain reaction, the safety of fission and the radioactive waste produced, and looks at the arguments for and against the use of nuclear power.
If teachers want to go into more detail about how nuclear reactors work then the TAP 528 episode on controlling nuclear fission is worth a look.
Dr Melanie Windridge's IOP Schools Lecture looks at the physics behind fusion reactions in the sun, and how JET is trying to use fusion for power on Earth. Highly recommended as an introduction to the topic of fusion.
This resource follows-on from the interactive Rutherford scattering animation, and contains discussion on the importance of Rutherford's experiment, and ideas for more practical investigations.
The follow-up to this episode, on the size of the nucleus, is located here.