Chapter 7.2 Half-Life: Nuclear Popcorn ActivityName:

Objective: Help students visualize the rate of radioactive decay.

Intended Learning Outcome:

  • Reason mathematically
  • Make predictions
  • Construct tables and graphs to describe and summarize data
  • Collect and record data
  • Understand science concepts and principles

Description

A simple way to simulate radioactive decay is by making popcorn. Popcorn starts out as unpopped “parent” kernels we’ll call “kernelite, (Ke).” Heating starts the radioactive decay clock and the “kernelite” begins to decay to a new daughter product of popped kernels we’ll call “popcornium, (Pc).” Just like radioactive decay, this process is irreversible, and with enough time all the kernelite will decay to popcornium. The “half-life” of kernelite is the time after which half of the kernels have popped, transforming to popcornium.

Materials:

  • Data Analysis sheet for each student
  • 6 un-popped mini bags of microwave popcorn
  • 4 mystery bags (Labelled A-D)

Procedure

  1. Using a microwave oven, pop 6 bags of popcorn one at a time.
  2. Label six of the bags with predetermined popping times t=0 sec, 10 sec, 20 sec, 30 sec, 40 sec, and 50 sec.Preset the microwave time for 2 minutes.
  3. Even though you will only be popping for a short time, some time will elapse as popcorn heats up and begins popping. The “radioactive decay” timing begins when you hear the first kernel of popcorn POP. Use the microwave timer or a stopwatch to measure the popping time. Turn the microwave off and remove the bag as soon as the predetermined (decay) popping time is reached.
  4. Each group will open a bag of popped corn, spread the contents on a large sheet of paper and carefully count and record the number of
  5. a) kernelite
  6. b) popcornium kernels. Record your results on the data sheet.

Nuclear Popcorn – Student Handout

Directions:

  1. Pop your bag of popcorn based on the instructions on the page above, ensuring you only pop it for the correct amount of time!Spread the contents on a large sheet of paper and carefully count and record the number of a) kernelite b) popcornium kernels. Record your results on the data sheet.
  2. Obtain Kernelite and Popcornium data from other groups. The complete the entire table below.

Calibration Samples

Bag Number / Popping Time (seconds) / Kernelite
Ke
(parent) / Popcornium
Pc
(daughter) / Total
Ke+Pc / % Ke (parent)
/ % Pc (daughter)

1
2
3
4
5
  1. Plot the results from bags with known popping time intervals on the graph with time (T) on the horizontal axis, % Kernelite (parent) ratio on the vertical axis (0-100% scale). On the same graph, also plot the % Popcornium (daughter) using the legend indicated.
  1. You can now determine the “half-life” of the Ke by finding the point where both % Ke and % Pc are 50% (where the two plotted lines cross) and reading the time from the horizontal axis.

Half-life of Ke: ______(seconds)

  1. Find the % Ke values from “unknown” bag and plot it on your decay curve above. Now, determine the unknown “age” (popping time) for your bag by reading the time from the X-axis that corresponds to the measured % Ke. Compare your results to the actual popping time as recorded by your teacher.

Unknown Samples

Bag Number / Kernelite
Ke
(parent) / Popcornium
Pc
(daughter) / Total
Ke+Pc / % Ke (parent)
/ % Pc (daughter)
/ Estimated Popping Time (seconds)

Discussion Questions

  1. What percentage of Kernelites were popped during the first half-life? During the second? Third?
  1. For each successive half-life, does the number of kernels that pops increase, decrease, or stay the same? If so, by how much?
  1. Suppose you have a JUMBO bag of popcorn with 1 million kernelites. Can you estimate how many kernelites will pop in the first half-life? Explain your answer.
  1. Inside the JUMBO bag there is a special blue Kernelite that follows all the same rules. Can you determine the half-life of this Kernelite? The seond half-life? Why or Why not.
  1. How did your estimated times in the unknown samples compare with actual times? How might scientists use this technique to determine the age of Dinosaurs? (*hint: Carbon 14 isotope)