Radioactive atoms are characteristically unstable, meaning that as they break down they give off radioactive particles (radioactivity) The particles break down to form an entirely different atom. For example carbon 14 decays to become nitrogen 14.
The 'half-life' of a given substance is the time it takes for half of the atoms it contains to decay (break down).
This practical allows students to understand this principle in a novel but effective manner.
Equipment Required (per set):
- 100 or so M&Ms or Skittles sweets
- Tub or box with lid
- Graph paper
The sweets must be either M&Ms or Skittles as one side of the sweet must be different from the other. Both M&Ms and Skittles have a logo printed onto one side of the sweet. The sweets are usually intended to be eaten by the student and so may need to be replaced each time. Dice or coins can be used instead of sweets. With dice, three sides may need to be painted or otherwise coloured.
The quantity of 100 is a guideline only. This practical can be conducted with any number of sweets, dice or coins although the more there are, the better the resultant graph.
Students set up all the sweets so that the logos are facing upwards. This represents the radioactive isotope. They then shake the box and place it flat on a desk. The sweets that still have the logo facing upwards represent atoms that have not decayed. The others represent atoms that have decayed and are therefore 'safe to eat'.
Roughly half of the sweets will fall logo up each time. This represents the half-life of the substance.
The student repeats the task, removing or eating the 'decayed atoms' until none are left. Each time the student can count the decayed atoms and record them in a table.
When finished the student should be able to produce a nicely curved graph.
Much of the appeal associated with this practical is that the students can eat sweets and learn at the same time. Ensure the sweets are fresh each time and they do not come into contact with desktops etc where they can be contaminated. If the sweets are not to be eaten but reused, be aware that the logos on the sweets rub off after time and will therefore not be usable after a few lessons.