GO IN DEPTH

# Radioactive Decay: A Sweet Simulation of Half-Life

PiccoloNamek [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

### Introduction

In this simulation, you will use small pieces of candy marked on one side. They will be your “nuclei.”  You also need a paper towel on which to place your “nuclei.”

## Procedure:

1. Count your nuclei (candy). Write that number in the data table under the heading “Number of Radioactive Nuclei.” In the column marked “Prediction for Next Toss” write the number of radioactive nuclei you think you will have with your next toss. (Radioactive nuclei will be those candies with the marked side down.)

2. Place your “nuclei” in a paper cup, cover and shake the cup. Pour the “nuclei” onto your paper towel. Separate the “nuclei” into two piles, one with the marked side up and the other with the marked side down. Count the number of “nuclei” in each pile. On your data table, record the number of “radioactive nuclei” candies with the marked side down. Predict how many radioactive “nuclei” you will have after the next toss.

3. Return only the radioactive “nuclei” to your paper cup. (You decide what to do with the “decayed nuclei,” or those with the marked side up.)

4. Continue this process until there are no radioactive “nuclei” left. Add more rows to your data table, if needed.

 Toss Number of radioactive nuclei Prediction for Next Toss 1 2 3 4 5 6 7 8 9 10 11

Analysis:
1. Using the pooled data, prepare a graph by plotting the number of radioactive “nuclei” on the y-axis and the number of tosses, which we will call half-lives, on the x-axis.
2. How good is our assumption that half of our radioactive “nuclei” decay in each half-life? Explain.
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3. If you started with a sample of 600 radioactive nuclei, how many would remain undecayed after  three half-lives? ___________________________________________________________________________
4. If 175 undecayed nuclei remained from a sample of 2800 nuclei, how many half-lives have passed?
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5. Why did we pool the class data? How does this relate to radioactive nuclei?
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6. How many half-lives would it take for 6.02 x 1023 nuclei to decay to 6.25% (0.376 x 1023) of the original number of nuclei?
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7. Is there any way to predict when a specific piece of candy will land marked side up or “decayed?” If you could follow the fate of an individual atom in a sample of radioactive material, could you predict when it would decay? Explain.
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8. Strontium-90 has a half-life of 28.8 years. If you start with a 10-gram sample of strontium-90, how much will be left after 115.2 years? Justify your answer.
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9. What do we mean by half-life? With what kinds of materials do we use this term?
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