Teaching radioactive decay & radiometric dating: an analog activity based on fluid dynamics

Erika Grundstrom
Vanderbilt University & Fisk University
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Radiometric dating/geochronology is a difficult concept for students. Using the (rather messy) medium of shampoo, students watch it flow through holes of different sizes, determine the exponential decay equation, then use this information to "date" the shampoo. This is an activity that is designed to help students understand exponential decay and primarily designed as a laboratory exercise, it could be modified to be a whole-class demonstration.
Developed by Lily Claiborne and Calvin Miller

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One version of the lab has been used in introductory geology for non-majors, another has been used with geology graduate students (the more complicated one), and it has been modified for early high school students.

Skills and concepts that students must have mastered

  • measurement
  • use of Excel would be nice, but not terribly necessary

How the activity is situated in the course

This is a stand-alone activity


Content/concepts goals for this activity

  • radioactive decay
  • exponential decay
  • using equations to predict
  • geochronology

Higher order thinking skills goals for this activity

analysis of data
synthesis of ideas

Other skills goals for this activity

using Excel for data analysis

Description of the activity/assignment

A fluid flowing from an upper beaker into a lower beaker (shampoo in this case) behaves mathematically identically to radioactive decay, mimicking the exponential decay process, dependent on the amount of fluid in the upper beaker (representing the amount of parent isotopes) and the size of the hole in the beaker (representing the decay constant). Students measure the fluid depth with time for several "runs" with varied conditions, then graph their results, create decay equations, manipulate these equations and use them to "date" another experiment. They then apply their new understanding to make predictions regarding complications involved in the decay process and its use in dating (such as daughter loss).

Developed by Lily Claiborne and Calvin Miller.

Determining whether students have met the goals

There's a pretest and a posttest included in the supplemental material. There are also plenty of test questions that pertain to radiometric dating

More information about assessment tools and techniques.

Teaching materials and tips

Other Materials

Supporting references/URLs

This is part of an accepted paper to Journal of Geoscience Education, URL to come when published.