All practice pages/Interatomic theory/Elements
Element 43, a transition metal
The first element made by people rather than found in nature, and today a workhorse of medical imaging.
Period 5, group 7. The other transition metals are tinted, and every cell opens its own article.
Every technetium atom is radioactive; it is the lightest element with no stable isotope. Chemically it resembles rhenium, the element below it.
Almost none exists on Earth; traces form in uranium ores when uranium atoms split. In 1952 the astronomer Paul Merrill found its spectral lines in red giant stars, proof that stars make heavy elements as they age, since any technetium present when those stars formed would have decayed long ago.
Mendeleev had left a gap for element 43, and several claimed discoveries turned out to be wrong. In 1937 Carlo Perrier and Emilio Segrè found it in a strip of molybdenum that had been bombarded in the Berkeley cyclotron. They named it from the Greek technetos, artificial.
Technetium-99m is injected for tens of millions of diagnostic scans a year, of bones, heart, brain and other organs. It gives off gamma rays a camera can see, and it has a half-life of only six hours, so it fades from the body quickly.
Radioactive. The tiny doses used in medicine are considered safe, but larger amounts are handled behind shielding.