⚛️ Atoms of radioactive elements are not eternal. They gradually decay and turn into atoms of other, lighter, chemical elements. Uranium becomes radium. Radium, undergoing 16 transformations, eventually passes into lead and helium. From one gram of uranium, after a sufficiently long period of time, 0.8653 grams of lead and 0.1345 grams of helium will be obtained. Missing to unity 0.0002 grams make up the mass that was spent on ☢️ radiation