Everything you wanted to know for the whole time about half-life in a quarter hour

funny - science - physics - radiation mutationSo we are studying Atomic & Nuclear Physics – one of the most exciting areas of modern physics, and almost certainly one of the sciences that has most affected human history in the 20th century. It is one of the areas of physics that the public knows the least about, despite a great deal of interest. Even popular culture deals with nuclear power – from “The Simpsons” to “Battlestar Galactica”, from Iron Maiden’s Brighter than a Thousand Suns to Andy Warhols “Atomic Bomb”, every form of human expression from highest art to puerile comedy, from heavy metal to science fiction – the idea is everywhere.

I have written many posts on this blog about nuclear power (1, 2, 3, 4, 5) (you may want to pay particular attention to the comment streams…). Not only is nuclear power an important part of our studies, it is essential that all people who live in Australia are aware of the risks and rewards associated with nuclear energy, because like it or not, Australia has a nuclear future. I have written a specific set of class notes to supplement your textbook. You must download them, print them and bring them to class.

This post is specifically about the concept of half-life (no, not the game). Half life is the name given to the process of atomic decay, and particularly the rate at which particles undergo the decay process. Half life is an interesting process – and works very differently from other types of decay.

Take an example that is probably more familiar – fruit. If you have a bag of apples, what happens over time?

Well – the apples rot of course, but think about how they rot – you wouldn’t expect to open the bag after one day and find half of them funny - science - physics - why to study physicsrotten and half of them untouched – and each day that half of what is left rots, while the other half is untouched. Atomic decay is exactly like this – which to the say the least, is a bit strange! Instead of having an amount of time after which they all decay – like food (think of the “best before” date), any radioactive material decays randomly – the only thing that is constant for any given radionuclide is that it has a known length of time in which 50% of the sample will undergo decay.

It is important to note that the process of decay does not result in particles “vanishing into thin air”. Just as with the bag of apples, a decayed (rotted) apple doesn’t disappear – it turns into something else (hopefully a nice apple pie, apple sauce, or a cider!). A radionuclide that decays turns into another atom – and is still present. We simply don’t count it – but it is still there – and may be undergoing another decay into another radionuclide (or possible stable nuclide).

The decay process will often take several steps before a radionuclide finally becomes stable, and thus stops being radioactive. This sequence of steps is called a decay chain and some examples are listed in your book. Here is another, more complicated one. You can explore any number of decay chains with this applet (link). This is similar to a diagram given in your handout notes, it shows areas of instability (and the type of radiation they create when they decay). Here is another link to a fantastic tool for you to explore decay chains – you must visit this one!

We can model half-life and radioactive decay mathematically – check these links (12, 3) for explanations and applets which show how the formula can be used. Final resource from me is a video – watch it and see how to work with the half life formula (please note that we are working with the simplest variation of the formula – there are many more that you can use!)

Now it is your turn – each of you must find a good resource that you like from anywhere, and share it with the class in the comments below. You must explain why you think it is good, and it would also be a marker of a good student if you used the comment thread to discuss resources that others find…

I’m sure you all want to show that you are good students, don’t you?

Because if you weren’t good students, I might have to spend an extended dose of one-on-one time with you, helping you to get better. During lunchtimes and after school, naturally.

So, be good – you wouldn’t like me when I get angry…

See you in class!

Explore posts in the same categories: Nuclear, Physics, Year 11

16 Comments on “Everything you wanted to know for the whole time about half-life in a quarter hour”

  1. Kyle Jarman Says:

    The links actually REALLY helped me understand how to use the formula properly. By resource i assume you mean something that will help us remember about half life, so here’s a graph that seems to simplify half lifes: http://ch302.cm.utexas.edu/images302/half-life-graph.jpg

  2. Connor Dickson Says:

    this link is from mr khan of khan academy, his handwriting may be bad but it is a pretty good walkthrough of half life


    • CyberChalky Says:


      It’s good to see you hunting up interesting resources – but like you say, Khan’s handwriting is dreadful, and sometimes I wonder if he is colour blind as well!

  3. Kyle Jarman Says:

    Are we aloud to bring a calculator into out Outcomes if we need it? Not a classpad but just a normal calculator. Thanks 🙂

  4. Aaron davis Says:

    i find this info chunk useful as it has a good graph about radioisotopic dating techniques

  5. Matt Pockett Says:

    This link was very helpful, it really cements what I have learnt about half-life.

  6. Matt Pockett Says:

    Here is the periodic table. Very helpful!

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