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Teacher Notes
Computer Activity: Understanding Half Lives
Teacher Notes
Introductory description of the investigations:
Student Handout
Student Solution
In the following investigation, the students use a physical model to gain
understanding of the radioactive decay process. Describe to the students
the activity and its purpose. In this activity, students model radioactive decay by gently
dropping colored disks into a drawer or box lid that has different colored regions. When a disk
falls into a like colored region it radioactively decays to a different colored disk. Since the
landing of disks on the patterned surface is random in the same way that radioactive decay is
random, the behavior of these two systems is very similar. The rules for this model are the
following:
• A disk landing on a like-colored surface decays into its daughter nuclide.
• A disk landing on different colored surfaces does not decay.
• Disks that do not match the grid colors do not ever decay and thus represent stable nuclei.
In this experiment, students drop red “nuclei” into the box lid. Each unstable red nucleus will
decay into a stable blue nucleus whenever it lands in a red region.
Emphasize that students should gently pour the cup of disks into the container so that the disks
stay within their container.
Variations on this activity:
• varying the area of colored regions varies the probability of decay.
• varying the number of colored regions and disks varies the number of decays before a stable
nucleus is formed.
Consider having students place red colored regions in the box lid on their own so that each box is
different. Once all groups have completed the experiment, bring the group together to discuss
the similarities and differences of their results.
Consider assigning the mathematical and/or nuclear forensic extensions at the end of the
lesson. Materials needed: graphing software and computer or graphing calculator.
Materials:
• ~100 blue disks
• ~100 red disks
• Cup
• Box lid
• Red colored paper pieces (small rectangles or circle)
• Glue stick
For the mathematical extension: Students will need access to graphing software such as excel
or a graphing calculator.
For nuclear forensic extension: This activity involves a decay chain. To reduce materials
needed you may want to create your box lids in the material list above with red, green, and plain
regions on the bottom and acquire 100 each of red, green, and blue disks