Radioactive Decay: A Sweet Simulation of Half Life



[pic] Radioactive Decay: A Sweet Simulation of Half Life

Name: _______________________________ Date: ____________ Period: __________

In this activity, Skittle candies represent atoms. All of the atoms begin as parent isotopes. Follow the directions below with your group to simulate their radioactive decay.

|Toss |Number of “unchanged” pieces |Prediction for next toss |

| |(radioactive parent isotope atoms) | |

|0 | | |

|1 | | |

|2 | | |

|3 | | |

|4 | | |

|5 | | |

|6 | | |

|7 | | |

|8 | | |

|9 | | |

Procedure:

1. Count your atoms. Write that number in the data table under the heading “Number of unchanged pieces (radioactive parent isotope atoms)” in the row for Toss 0. In the column marked, “Prediction for next run” write the number of radioactive atoms you think you will have with your next toss. (Radioactive parent isotopes will be represented by the Skittles with the printed S facing down, and the daughter isotopes will be represented by Skittles with the printed S facing up.)

2. Place your atoms in a paper bag, hold the top closed, and shake the bag three times. Pour the “atoms” onto your paper plate so that they are spread out rather than in a pile. Pick up and set aside ONLY the candies with the S side up (daughter isotopes). These will not go back into the bag since they are the decayed isotopes. Count the number of “parent isotopes” or S side down that did not change to daughters during the first toss.

3. Record the Skittles that had the S side down. The Skittles with S side down are to be replaced by an equal number of marshmallows. Put these marshmallows in the bag along with the remaining “parent isotopes.” The marshmallows represent the decayed daughter isotopes. (You decide what to do with the “daughter isotopes Skittles” that you set aside. Hint: You could eat them since they are decayed!)

4. Continue this process until you have completed nine tosses where you remove the daughter isotopes that have decayed. Don’t forget to record the number of parents after each toss and to replace the decayed “daughter isotopes” with marshmallows. (wait quietly while all the groups finish up their 9 tosses.)

5. Once all groups are finished, we will combine the class data to complete the chart below.

|Toss |Class Total |Number of “unchanged” pieces (radioactive parent isotope atoms) |Class Average |

| |Team 1 |Team 2 |Team 3 |Team 4 |Team 5 |Team 6 |Team 7 |Team 8 | | |1 | | | | | | | | | | | |2 | | | | | | | | | | | |3 | | | | | | | | | | | |4 | | | | | | | | | | | |5 | | | | | | | | | | | |6 | | | | | | | | | | | |7 | | | | | | | | | | | |8 | | | | | | | | | | | |9 | | | | | | | | | | | |

Analysis:

Create a line graph on the graph paper the teacher provides that shows the number of parent isotopes remaining after each toss. Connect each successive point on the graph with a blue line.

On the same graph, each team should plot the AVERAGE VALUES for the class as a whole and connect that with a red line.

Finally, on the graph, each group will plot the points that represent the true half life number of parent isotopes. Example: 100 ÷ 2 =50 50÷2= 25 (This represents exactly 50% of the parent isotopes decaying with each toss). Connect these points with a green line

When you have completed your graph, answer the following questions with your group.

1. What does each toss represent?

2. Why do you think it was necessary to replace the Skittles that landed with the S facing down with marshmallows instead of just removing them?

3. Why didn’t each group get the same results?

4. Which of the following goes with the mathematically calculated line on the graph (green one) the best: (a) your group’s results line or (b) the line based on the class average? Why?

5. How good is our assumption that half of our parent atoms decay in each half-life? Explain.

6. If you started with a sample of 600 radioactive atoms, how many would remain undecayed after three half-lives? (Show the math)

7. If 175 undecayed atoms remained from a sample of 2800 atoms, how many half-lives have passed? (Show the math)

8. A) Why did we pool the class data?

B) How does this relate to radioactive atoms?

9. A) Is there a way to predict when a specific piece of candy will land marked side up or “decayed?”

B) If you could follow the fate of an individual atom in a sample of radioactive material, could you predict when it would decay? Explain.

10. 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? (Show the math).

11. A) Explain what is meant by half-life?

B) What kinds of materials do we use with the term half-life?

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