1. Module 8

1.15. Page 6

Lesson 2

Module 8—Nuclear Decay, Energy, and the Standard Model of the Atom

 

Lesson Summary

 

In this lesson you focused on the following questions:

  • What is a half-life?
  • How are half-lives used to determine age?

In this lesson you learned that the half-life of a radioactive isotope is defined as the amount of time it takes for half of the radioactive nuclei to decay. Graphing the amount of parent nuclei versus time gives the following mathematical expression for the number of original parent nuclei in a radioactive sample after a given time interval.

 

Half-life curve showing original number of parent nuclei and amount after one half-life.

 

 

 

 

 

 

 

 

 

 

 

 


 

Both the graphical representation and the mathematical expression can be used to determine the age of a radioactive sample. Radioactive dating is based on comparing the remaining amount of parent nuclei to the amount that was originally in the sample. Using this and the known half-life of the material, it is possible to accurately determine its age.

 

Lesson Glossary

 

activity or decay rate: the number of nuclei in a sample that decays in a given time interval

 

becquerel (Bq): the unit of radioactivity equal to one decay per second

 

half-life: the time it takes for half the radioactive nuclei in a sample to decay