To do this lesson and understand half-life and rates of radioactive decay, students should understand ratios and the multiplication of fractions, and be somewhat comfortable with probability.
If they haven't changed their answers, ask them to explain why.
In addition to using answers to students' analysis questions and their graphs for assessment, consider having them respond to the following in their science journals or as a homework assignment: Strontium is chemically similar to calcium.
Include your ideas about how its half-life of 28.8 years would be important.
Suggest ways that government agencies, such as your state's department of health, might test for strontium-90.
It may be combined with the Frosty the Snowman Meets His Demise: An Analogy to Carbon Dating, which can be done while students are flipping their candies.
In your planning, be sure to include time at the end of the lesson for students to post their data and share the class data.
To demonstrate that the rates of decay of unstable nuclei can be measured, that the exact time that a certain nucleus will decay cannot be predicted, and that it takes a very large number of nuclei to find the rate of decay.
This is the second lesson in a three-lesson series about isotopes, radioactive decay, and the nucleus.
To help students understand the history of radioactivity, have them go to Radioactivity: Historical Figures, on the Access Excellence Classic Collection site, to read about the contributions of Wilhelm Roentgen, Antoine Becquerel, Marie and Pierre Curie, and Ernest Rutherford.
As students read about these scientists, ask them to think about the following questions: Students can supplement this site with a visit to Isotopes Project.
Have students look at the Glossary of Nuclear Science Terms for alpha and beta decay.