Part a) You are using a Geiger counter to measure the activity of a radioactive substance over the course of several minutes. If the reading of 400 counts has diminished to 100. counts after 59.4 minutes, what is the half-life of this substance?
Part b) An unknown radioactive substance has a half-life of 3.20 hours. If 46.0 g of the substance is currently present, what mass was present 8.00 hours ago?
Part c) Americium-241 is used in some smoke detectors. It is an alpha emitter with a half-life of 432 years. How long will it take in years for 41.0 percent of an Am-241 sample to decay?