technetium (redirected from Technetium compounds)

technetium (tĕknē`shēəm) [Gr. technetos=artificial], artificially produced radioactive chemical element; symbol Tc; at. no. 43; mass no. of most stable isotope 98; m.p. 2,200°C;; b.p. 4,877°C;; sp. gr. 11.5 (calculated); valence +4, +6, or +7. Technetium is a radioactive silver-gray metal. In some of its chemical properties it resembles rhenium, the element below it in Group 7 of the periodic table. It tarnishes slowly when exposed to moist air. Although it is not attacked by hydrochloric acid, it dissolves in concentrated sulfuric or nitric acid and in aqua regia. The pure metal may be prepared by chemical reduction of certain of its compounds with hydrogen gas. Potassium technetate, KTcO₄, has found some use in alloys with iron and steel; the addition of a small amount renders the alloy highly resistant to corrosion. This use is limited by the radioactivity of the element. The most stable isotope, technetium-98, has a half-life of 4.2 million years; most of the other 30 known isotopes are much less stable. Technetium-95m is a gamma-ray emitter with a half-life of 61 days that is used in radioactive tracer studies. The most useful isotope of technetium, however, is technetium-99m, which is used in many medical radioactive isotope tests because of its short half-life (6.01 hours), the energy of the gamma radiation it emits, and its ability to bind chemically to many biologically active molecules. Technetium was once very rare and expensive but is now obtained in quantity from nuclear reactor fission products. Although the spectra of some stars show that they contain technetium, the naturally occurring element has not been found on earth. It is called technetium because it was the first element to be prepared synthetically. Its existence was predicted from the periodic table. Discovery of the element in nature was erroneously claimed in 1925 by the German chemists I. W. and W. K. Noddack, who called it masurium. The element was discovered in 1937 by C. Perrier and E. G. Segrè of Italy in a sample of molybdenum that was bombarded with deuterons in a cyclotron at the Univ. of California at Berkeley and sent to them by E. O. Lawrence.

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technetium

Metallic chemical element, one of the transition elements, chemical symbol Tc, atomic number 43. All its isotopes are radioactive (see radioactivity); some occur in trace amounts in nature as nuclear fission products of uranium. Its isotope technetium-97 was the first element artificially produced (1937; see cyclotron). Technetium-99, a fission product of nuclear reactors that emits gamma rays, is the most-used tracer isotope in nuclear medicine. Technetium resembles platinum in appearance and manganese and rhenium in chemical behaviour. It is also used as a metallurgical tracer and in corrosion-resistant products.

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technetium

a silvery-grey metallic element, artificially produced by bombardment of molybdenum by deuterons: used to inhibit corrosion in steel. The radioisotope technetium-99m, with a half-life of six hours, is used in radiotherapy. Symbol: Tc; atomic no.: 43; half-life of most stable isotope, ⁹⁷Tc: 2.6 × 10⁶ years; valency: 0, 2, 4, 5, 6, or 7; relative density: 11.50 (calculated); melting pt.: 2204°C; boiling pt.: 4265°C

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technetium [tek′nē·shē·əm]

(chemistry)

A transition element, symbol Tc, atomic number 43; derived from uranium and plutonium fission products; chemically similar to rhenium and manganese; isotope⁹⁹Tc has a half-life of 200,000 years; used to absorb slow neutrons in reactor technology.

(metallurgy)

Silver-gray metal with a high melting point, slightly magnetic.