I teach Modern Physics here at CSUC, and we occasionally use isotopes with half-lives of a year or less (such as Zinc-65 and Cadmium-109) for energy-calibration sources for a gamma-spectroscopy lab. I thought it might be fun to try measuring the activity of one of these sources over time and thus get a looooong-scale half-life data-set for students to play around with. Or maybe watch background nuclear coun ...