Polonium

Polonium is a rare, intensely radioactive element with a metallic appearance; it is sometimes classified as a metalloid. Only tiny traces occur naturally, forming as uranium decays in uranium ores, so these ores are not useful sources. Most polonium for research and specialized applications is made by irradiating bismuth in a nuclear reactor. Its radioactivity releases energy as heat: polonium-210 heat sources helped keep instruments warm on Soviet Moon rovers during the lunar night. Polonium has also been used in devices that reduce static electricity, though safer alternatives have replaced many of them. Because its radiation is hazardous, its uses are limited and require specialized controls.