Radioactive Decay and Geochronology
Students create a STELLA model of the radioactive decay process. They then learn how the special radioactive series 238U - 206Pb and 235U - 207Pb 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.
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)
Teaching Notes and Tips
Instructor Notes (Acrobat (PDF) 44kB Apr10 06)
Radioactive_Decay_Lab-Answer_Key.pdf (Acrobat (PDF) 213kB 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.