Ellery Frahm made a good comment on the last entry. Measuring radioactive decay is a great way to help students understand radiometric dating, not to mention data collection, graphing, and analysis. I do have a lab with my archaeometry course, and we will be doing an activity in two weeks on radioactive decay. We use an isotope generator made by Spectrum Techniques, which generates a low-level radioactive 137Ba isotope, which has a half-life of just under 3 minutes. The emitted gamma rays may be readily detected using a Geiger-Muller or scintillation radiation detector.
Below are some of my test results.