Technetium, a silverygray, metallic chemical element, formerly called masurium. Scientists have identified technetium in the spectra of certain stars, which are believed to produce technetium by internal nuclear processes. The element has not been found to occur naturally on earth. It is obtained as a by-product from the fission of uranium and plutonium in nuclear reactors.

All technetium isotopes are radioactive. The longest-lived technetium isotope, technetium 97, has a half-life period of about 2,600,000 years. Technetium 99m, a form of technetium 99 with a half-life period of about 6 hours, is used as a radioactive tracer to study the functions of the thyroid gland, spleen, and circulatory system, and to locate tumors in the liver, kidneys, and brain. Technetium is also used as a corrosion inhibitor for steel.

Technetium was the first chemical element to be produced artificially. (Its name is derived from a Greek word meaning artificial.) Working in Italy in 1937, Emilio Segr and Carlos Perrier discovered technetium in a sample that had been prepared at the University of California by bombarding molybdenum with deuterons.

Symbol: Tc. Atomic number: 43. Atomic weight of most stable isotope: 98. Specific gravity: 11.50. Melting point: about 3,940 F. (2,171 C.). Boiling point: about 8,820 F. (4,882 C.). Technetium has 16 isotopes: Tc-92 through Tc-107. It belongs to Group VII-B of the Periodic Table and can have a valence of +4, 5, 6, or 7.