# Radioactive Decay and Geochronology

**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: May 3, 2006

#### Summary

Students create a STELLA model of the radioactive decay process. They then learn how the special radioactive series 238U - 206Pb and 237U - 205Pb can be used to determine both the time when a rock initially crystallized and when it underwent a recrystallization, even when the sample being dated was not a closed system.

## Learning Goals

The Radioactive Decay exercise has several purposes:

- To convey concepts necessary in modeling a system involving exponential growth and decay
- To introduce elementary differential equations
- To convey the difference between closed and open systems
- To introduce if-then-else logical statements
- To convey the importance of secular equilibrium, which allows complex isotopic decay systems to be modeled without taking into consideration radioactive daughters.
- To explore concordia-discordia diagrams and how a rock containing two isotopic systems can yield both the age of original crystallization and the time of a later metamorphic event.

## Context for Use

This activity was developed for a class introducing dynamical systems modeling to upper level undergraduate students.

## Description and Teaching Materials

radioactive_decay_lab-student_version.pdf (Acrobat (PDF) 38kB Jun13 05)

Documented_Isotope_Model.stm ( 25kB Jun13 05)

Documented_UPb_Model.v.1.STM ( 589kB Jun13 05)

Documented_UPb_Model.v.2.stm ( 705kB Jun13 05)

PBLOSS.F90 ( 4kB Jun13 05)

U_series.f90 ( 4kB Jun13 05)

fortran_radioactive_decay.pdf (Acrobat (PDF) 8kB Jun13 05)

Documented_Isotope_Model.stm ( 25kB Jun13 05)

Documented_UPb_Model.v.1.STM ( 589kB Jun13 05)

Documented_UPb_Model.v.2.stm ( 705kB Jun13 05)

PBLOSS.F90 ( 4kB Jun13 05)

U_series.f90 ( 4kB Jun13 05)

fortran_radioactive_decay.pdf (Acrobat (PDF) 8kB Jun13 05)

## Teaching Notes and Tips

Instructor Notes (Acrobat (PDF) 44kB Apr10 06)

## Assessment

Radioactive_Decay_Lab-Answer_Key.pdf (Acrobat (PDF) 213kB Jun13 05)

assignment_assessment_2.pdf (Acrobat (PDF) 5kB Jun13 05)

assignment_assessment_2.pdf (Acrobat (PDF) 5kB Jun13 05)

## References and Resources

The following are readings for this activity:

- Dalrymple, G.B., 1991, The Age of the Earth, Stanford, CA: Stanford University Press, p. 79-90, 99-102, 115-119, and 122-124.
- Faure, G., 1986, Principles of Isotope Geology, 2nd Edition, New York: John Wiley and Sons, p. 38-45 and p. 283-296.