Radioactive Decay!

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Updated on Feb 06, 2012

Grade Level: 7th - 8th; Type: Physics

Construct a model of radioactive decay.

  • What is radiation?
  • What is nuclear medicine?
  • What is decay rate?
  • What is an isotope?
  • What is meant by the half life of a radioactive isotope?
  • How is carbon- 14 dating used?
  • What is meant by concept of probability?
  • Do you think the use of coins and probability theory might or might not be effective in modeling radioactive decay?
  • What is transmutation?

On the information level, the student will be using concrete, hands on model to demonstrate the meaning of half –life in the process of radioactive decay. The chances that a single atom of uranium -238 will decay during a one minute period are indeed very low. However, in contrast, the chances that an atom of polonium-214 will decay during one minute are very high.Every radioactive isotope has its own rate of decay. This rate is called and measured as a half life. A half life of an isotope is defined as the amount of time it takes for half of the atoms in the sample to decay. Half lives can be as short as milliseconds and as long as billions of years. For example, were we to examine lead-214, we would find a half life of 27 minutes. After the first 27 minute, we would find that we were left with some bismuth 214 as well as lead-214.

In this science project, each coin represents an atom. A coin has a 50 percent chance of showing heads, so in any round we would expect approximately half the coins to show heads. This corresponds to the decay of half the atoms in a radioactive substance and therefore the coins are indeed a good model.On a process level, the student will be using the scientific method to test and observe the pattern of the coin sample and extrapolate the” half life “of the coin sample from the obtained data.Hopefully, the result is a clear- cut operational concept of the half- life of radioactive substances.

  • 100 pennies
  • pen
  • paper
  • a bag to hold the coins

  1. Gather all the materials you will need for this project. These include 100 coins, pen, paper and a strong paper or plastic bag for your coins. You may wish to include a camera and take photos of the steps as you go though the experiment.
  2. Copy the Data Chart provided below so that you can readily record your observations.
  3. Put the coins in the bag. Close the bag securely and shake the bag.
  4. Now spill the coins out on the table in front of you. Do not lose any! You may want to snap a photo.
  5. Gather and count all the coins that are heads. Put them aside. In the Data Chart record this number of coins in the column Coins Removed.Now subtract and calculate the number remaining and put that number in the Coins Remaining column.
  6. Now collect the coin that were tails and put them back in the bag .Close the bag and shake!
  7. Repeat steps 4,5and 6 until you have run out of coins to put back in the bag
  8. Now take the data you have and draw a bar graph showing what happened to the size of your coin sample as went through all of the steps.
  9. Review all of your data. Write up your report by responding to the following questions: Explain what each coin represents. Note how many times you had to toss the coins before they were all used up. Did you find a pattern? What does the bar graph show?
  10. Think about it! If you repeated this experiment again, do you think you would get the same or different results? Why?
  11. Explain why this experiment was useful in replicating a model of radioactive decay. Why were the coins a good way to model half-lives? Would the model work as well if we used 1000 coins?At what point should we be concerned with transmutation?

Data Chart


# of Coins Removed

# of Coins Remaining











Terms/Concepts: radiation; nuclear medicine; isotopes; radioactive decay; decay rate; half-life; carbon 14 dating; transmutation


Dr. Muriel Gerhard (Ed.D.) is a retired educator with fifty seven years of experience in all aspects of public education. She has been a teacher, principal, administrator, college professor, researcher, grants writer, change agent and science editor. She is the author of several books on education used as college texts. These include the best selling Effective Teaching Strategies with the Behavioral Outcomes Approach and The Behavioral Outcomes Handbook for Teachers and Administrators. Presently she is a consultant in science education and curriculum development, a marriage and family therapist, a newspaper columnist and an author. Her latest book, recently published, is a memoir of sixty vignettes entitled âNow That I`m Dead, I Decided to Write this Bookâ.