Using Popcorn to Simulate Radioactive Decay

Jennifer Wenner, University of Wisconsin-Oshkosh, wenner@uwosh.edu
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Initial Publication Date: February 25, 2006

Summary

Popping popcorn in your class is an excellent way to illustrate both the spontaneity and irreversible change associated with radioactive decay. It helps students to understand the unpredictability of decay.

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Learning Goals

Related Links

  • to illustrate the unpredictability and spontaneity of radioactive decay
  • to help students to understand that the decay of one atom to another is irreversible

Context for Use

This is an in-class demonstration. I usually perform it after I have introduced radioactive decay and talked about how it works. It only takes a few minutes and I usually talk while I am waiting for the "decay" to happen.

Required equipment includes popcorn, vegetable oil, a pan and a hot plate (a hot air popper or other popcorn popper would work too). If you're doing it the old-fashioned way (pan and hot plate), a bit of newspaper would be a good idea, too, as I like to leave the top of the pan off and the oil can splatter a bit.

Description and Teaching Materials

Popcorn popping is a great analogy for the spontaneity of radioactive decay. It is impossible to predict which kernel will pop first. If you can, bring in a hotplate, a small pan, oil and some popcorn. Put the oil in the pan with a few kernels of popcorn.
  • Ask the students to predict which will pop first.
  • What are variables that control whether a kernel of corn will pop?
  • What happens to the kernel of corn when it does pop? Can it go back to the way it was before it popped?

Teaching Notes and Tips

If you decide to go with the pan, oil and hot plate (as opposed to air popper), there are a few things I recommend:
  1. Put only a few (5 or so) kernels in to start.
  2. Leave the top of the pan off. Students get a kick out of seeing the popcorn go flying. It makes it more exciting for you, too -- I always miscount and end up getting scared by the last kernel.
  3. Put some newspaper under the hotplate so that oil doesn't get everywhere. The first time I did this, I made a pretty big mess on the lab bench.
  4. After the initial "decay" and if your class isn't too large, pop some more (with the lid on) so that students can enjoy the demonstration too

Assessment

A quick check of whether the students picked up the ideas of unpredictablitly and irreversibility can be done in one of several ways.
  • A one or two question quiz, with questions that relate to the goals of this exercise.
  • A short group discussion (in small groups or as a whole class) about the analogy of popcorn and how it is like radioactive decay.
  • If you are moving on to talk about radiometric dating or half-life, intersperse your lecture with questions about the analogy

References and Resources

Lisa Tauxe at Scripps has another discussion -- you have to scroll down about halfway to What does popcorn have to do with it? (more info)