Americium-241 is used in smoke detectors. It has a first-order rate constant for radioactive decay of k=1.6×10−3yr−1
By contrast, iodine-125, which is used to test for thyroid functioning, has a rate constant for radioactive decay of k=0.011 day −1
How much of a 1.00-mg sample of each isotope remains after three half-lives?