The half-life of radioactive radium-226 is about 1599 years. That is, for a given amount of radium, half of the original amount will remain after 1599 years. After another 1599 years, one-quarter of the original amount will remain, and so on. Let represent the mass, in grams, of a quantity of radium. The quantity present after years, then, is t 1 1599 :25 _ y [2]