Half-life activity

You will need

• • Bag of M&Ms or Skittles or any lollies with writing on one side.

  • A4 graph paper, A3 white paper

  • Marker pen

  • Ruler

  • snap lock bag

What to do

Make an estimate of how many trials will take to have zero lollies if you remove approximately half each trial

• • Count the lollies (use about 40) into the snap lock bag

  • Set up the axis on your graph , with is number as your maximum, try to use the full length of the paper,

  • Shake the bag and then poor the lollies onto a sheet of A3 paper

  • Remove all he lollies with letter side up, counting them and putting them back in the bag

  • annotate your graph with the number replaced in the bag, this is trial 1.

  • repeat this process until there are no lollie to put back in the bag

What’s happening?

It probably took about eight rounds before all the lollies landed letter up. You may find that surprising, since half the lollies were letter-up after the first round. The average ‘lifespan’ for a lolly in this activity is about 1.5 rounds, yet some lollies may survive four or five times longer!

This sort of process, where a quantity keeps halving, is called exponential decay. The most famous example of exponential decay is found in radioactive materials. Every radioactive substance has a half-life, the length of time it takes for half its atoms to decay.

Discussion

1. What does the x-axis represent in this example?

2. What does the y-axis represent?

3. How could a graph like this be used to find out information about a radioisotope?