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Using Stable Isotopes to Determine Material Origin (2 Favorites)

ACTIVITY in Atoms, Isotopes, Alpha/Beta/Gamma Decay, Subatomic Particles, Radioactive Isotopes. Last updated January 17, 2020.


Summary

In this lesson, students will review the concept of isotopes and apply the concepts of stability and relative abundance in order to determine the recent travels of a person of interest in a criminal investigation.

Grade Level

High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

  • HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data
    • Engaging in Argument from Evidence

Objectives

By the end of this lesson, students should be able to

  • Calculate the number of subatomic particles in different isotopes
  • Calculate an element’s atomic mass based on relative abundance and mass numbers
  • Define stable isotope
  • Predict the origin of materials based on isotope analysis

Chemistry Topics

This lesson supports students’ understanding of

  • subatomic particles
  • atomic mass
  • isotopes
  • relative abundance
  • nuclear stability

Time

Teacher Preparation: 15 minutes

Lesson: 60 minutes (about 20 minutes per worksheet)

Materials

Safety

No safety precautions needed

Teacher Notes

  • The majority of this activity is a standard review of subatomic particles and initial lessons in isotopes and relative abundance.
  • The “Isotopes & Calculating Average Atomic Mass” Simulation is used to help students calculate atomic mass.
  • Teacher may wish to stop before extension and give examples of how the stable isotope maps work, perhaps pulling in another example (strontium example is listed in references) – this is particularly good for extensions. More information about the maps can be found in the “Teacher Notes 1” download in the sidebar.
  • In the maps used, the ratios (R) are for hydrogen (2H/1H) and oxygen (18O/16O). In most of the US, there is less deuterium than in the standard (δ2H is negative); there is more 18O than in the standard (δ18O is positive).
  • The problem given on the worksheet is a bit more complex. A hair is found at a crime scene in central Wyoming. This area is part of the very dark blue sections of both maps and is a distinctive geographic region. The analysis of the hair shows that the end (the oldest part) originates from a bright red region in both maps – again distinctive.
  • It is suggested that the teacher takes the students through a few different places – figuring out the deltas for those locations. Then, start the map, showing how the first one is from a dark blue area on both maps and locating that area.
  • There are many potential paths through the US, but the source can only be Central Texas.There is one very logical straight line, but if a student supports his or her path with the correct isotope data, the student’s path should be considered correct. This is the path I drew (expand to see white dot path:

For the Student

Download all documents for this lab, including the teacher guide, from the "Downloads box" at the top of the page.