Technetium

Technetium is a silvery-gray metal and the lightest element with no stable form: every one of its isotopes is radioactive. Any that existed when Earth formed decayed long ago, so it was the first element to be made artificially, by Carlo Perrier and Emilio Segrè in 1937. Its name comes from the Greek for artificial. Tiny traces do occur naturally in uranium ores.

Its main use is in medicine. A short-lived form, technetium-99m, gives off gamma rays that a special camera can detect, then fades away within a day or so. Injected in tiny amounts, it lets doctors image bones, the heart and other organs in tens of millions of scans every year.