Starting Point-Teaching Entry Level Geoscience > Interactive Lecture Demonstrations > Examples of Teaching with Demonstrations > Half Life Model
Explore Teaching Examples | Provide Feedback

Half Life Model

David N. Steer (steer@uakron.edu)and Kyle Gray (krg10@uakron.edu), University of Akron
This material is based upon work supported by the National Science Foundation under Grant No. GEO-0506518.

This activity was selected for the On the Cutting Edge Exemplary Teaching Collection

Resources in this top level collection a) must have scored Exemplary or Very Good in all five review categories, and must also rate as “Exemplary” in at least three of the five categories. The five categories included in the peer review process are

  • Scientific Accuracy
  • Alignment of Learning Goals, Activities, and Assessments
  • Pedagogic Effectiveness
  • Robustness (usability and dependability of all components)
  • Completeness of the ActivitySheet web page

For more information about the peer review process itself, please see http://serc.carleton.edu/NAGTWorkshops/review.html.

This page first made public: Aug 25, 2008


While working in groups to facilitate peer tutoring, students manipulate a hands-on, physical model to better comprehend the nature of half life. Students use the model to simulate the decay of radionuclides. The resulting data are graphed and used to calculate ages in several hypothetical scenarios.

Learning Goals

Students will understand

Context for Use

This model works well with groups of two to four students. The time required to complete this activity may be longer than desired for a large, undergraduate lecture class, but is well suited for an undergraduate laboratory class or secondary science class.

Teaching Materials

Each student model consists of the following materials:
Half Life Model

During a lecture, have the student groups place the washers into the box silver side up. (The silver side represents the parent and the gold side represents the daughter product.) Students record the number of silver washers (50 parent isotopes) in the box. After closing the lid, students shake the box five times, open the box and count the number of silver washers. After recording the number of silver washers in the box as well as the cumulative number of gold washers, the students remove the gold washers, replace the lid, and shake the box again. This process is repeated until zero silver washers in the box.

Students use the data collected and the colored pencils to graph the number of silver and gold washers for each trial and label each curve as the parent or daughter. They also answer an assessment question (See handout (Microsoft Word 40kB Aug19 08)).

After debriefing the exercise, draw a graph using the average number from each trial. This curve will be very close to the theoretical value. (After our first semester of using this model, we used data from a previous class to calculate the average values for each trial.) Explain how any one group might have results that are different from the theoretical value, but when the data from the entire class are averaged together, the results match the expected values. This can lead into a discussion on the randomness of radioactive decay.

Teaching Notes and Tips

Some groups may experience the following problems:


Several different assessment techniques can be used depending on time and the needs of your class.

References and Resources

Worksheet (Microsoft Word 40kB Aug19 08) used with this model
Archived ConcepTest questions used with this model: Other Half-Life Activities:


Geoscience:Geology:Geochemistry:Radioisotopes, Geoscience:Geology:Geochemistry

Resource Type

Activities:Classroom Activity:Short Activity:Demonstration, Activities

Grade Level

College Lower (13-14):Introductory Level

Earth System Topics

Solid Earth:Earth Materials


Geochemistry:Radioisotopes, Time/Earth History


Teach the Earth:Teaching Environments:Intro Geoscience, Teach the Earth:Course Topics:Geochemistry

See more Examples of Teaching with Demonstrations »