Technetium Tc

Discovery

Mendeleev left a gap below manganese for "eka-manganese", and for more than half a century chemists searched minerals for it. In 1925 Walter Noddack, Ida Tacke and Otto Berg reported finding it by X-ray spectroscopy and named it masurium, but others could not reproduce their results and the claim was not accepted.

In 1937 Emilio Segrè and Carlo Perrier at the University of Palermo analysed a molybdenum foil sent by Ernest Lawrence from Berkeley. The foil had been bombarded with deuterons in a cyclotron, and the two chemists separated radioactive isotopes of element 43 from it.

In 1952 the American astronomer Paul Merrill detected technetium absorption lines in the spectra of certain red giant stars. Because technetium's half-lives are far shorter than the ages of those stars, its presence showed that heavy elements are being made inside stars today, strong support for the theory of stellar nucleosynthesis.

Origin of the name

The name comes from the Greek technetos, "artificial", honouring its status as the first human-made element; it was adopted around 1947. The symbol is Tc.

Main uses

• Nuclear medicine: technetium-99m emits a single gamma ray of about 140 keV and has a half-life of about six hours, giving clear images with a relatively low radiation dose. It is used for bone scans, heart perfusion studies and imaging of the thyroid, kidneys and lungs.
• Supply: hospitals draw technetium-99m as needed from "technetium generators" that contain decaying molybdenum-99.
• Corrosion research: the pertechnetate ion inhibits corrosion of steel at very low concentrations, but its radioactivity limits this to closed systems.

Isotopes

Technetium is the lightest element with no stable isotopes. Its longest-lived isotopes, technetium-97 and technetium-98, have half-lives of roughly 4.2 million years, which is why its atomic weight is shown in brackets as [97].

Technetium-99, with a half-life of about 211,000 years, is produced in large quantities by uranium fission and is a long-term concern in spent nuclear fuel. Medical technetium-99m is an excited state of technetium-99 that releases a gamma ray and becomes ordinary technetium-99.

In everyday life

In nature technetium forms only in trace amounts through spontaneous fission in uranium ores, so it cannot be mined; it is made in nuclear reactors. Only a handful of reactors worldwide produce molybdenum-99, and maintenance shutdowns have repeatedly caused shortages that disrupted hospital scanning schedules.

Because technetium-99m decays quickly, most of its activity is gone within a day, and much of it leaves the body in urine. That is why patients are often advised to drink plenty of fluids after a scan.