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Definition: technetium from The Penguin Dictionary of Science

Symbol Tc. The element with atomic number 43 and most stable isotope 98, which is in the second row of the d-block elements in the periodic table. Its name is derived from the Greek for ‘artificial’, which is appropriate as it does not occur naturally. All its isotopes are radioactive, the nuclide 99Tc having clinical use for scanning bones and organs.

Summary Article: technetium
From The Columbia Encyclopedia

(tĕknē'shēӘm) [Gr. technetos=artificial], artificially produced radioactive chemical element; symbol Tc; at. no. 43; mass no. of most stable isotope 98; m.p. 2,200 degrees Celsius; b.p. 4,877 degrees Celsius; 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.

The most stable isotope, technetium-98, has a half-life of 6.6 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. 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.

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.

The Columbia Encyclopedia, © Columbia University Press 2018

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