Technetium Information
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Technetium Element
Technetium is a chemical
element with the symbol Tc and atomic number 43. It is the lightest element
whose isotopes are all radioactive; none are stable other than the fully
ionized state of 97Tc.[4] Nearly all available technetium is produced as a
synthetic element, and only about 18,000 tons are estimated to exist at any
given time in the Earth's crust. Naturally occurring technetium is a
spontaneous fission product in uranium ore and thorium ore, the most common
source, or the product of neutron capture in molybdenum ores. This silvery
gray, crystalline transition metal lies between manganese and rhenium in group
7 of the periodic table, and its chemical properties are intermediate between
those of these two adjacent elements. The most common naturally occurring
isotope is 99Tc.
Element 43 was predicted on the
basis of the periodic table, and was erroneously reported as having been
discovered in 1925, at which time it was named masurium. The element was
actually discovered by Perrier and Segre in Italy in 1937. It was found in a
sample of molybdenum, which was bombarded by deuterons in the Berkeley
cyclotron, and which E. Lawrence sent to these investigators. Technetium was
the first element to be produced artificially. Since its discovery, searches
for the element in terrestrial material have been made. Finally in 1962,
technetium-99 was isolated and identified in African pitchblende (a uranium
rich ore) in extremely minute quantities as a spontaneous fission product of
uranium-238 by B.T. Kenna and P.K. Kuroda. If it does exist, the concentration
must be very small. Technetium has been found in the spectrum of S-, M-, and
N-type stars, and its presence in stellar matter is leading to new theories of
the production of heavy elements in the stars.
Many of technetium's properties
were predicted by Dmitri Mendeleev before the element was discovered. Mendeleev
noted a gap in his periodic table and gave the undiscovered element the
provisional name ekamanganese (Em). In 1937, technetium (specifically the
technetium-97 isotope) became the first predominantly artificial element to be
produced, hence its name (from the Greek τεχνητός, meaning "synthetic or
artificial", + -ium).
One short-lived gamma
ray-emitting nuclear isomer of technetium—technetium-99m—is used in nuclear
medicine for a wide variety of diagnostic tests, such as bone cancer diagnoses.
The ground state of this nuclide, technetium-99, is used as a gamma-ray-free
source of beta particles. Long-lived technetium isotopes produced commercially
are by-products of the fission of uranium-235 in nuclear reactors and are
extracted from nuclear fuel rods. Because no isotope of technetium has a
half-life longer than 4.21 million years (technetium-97), the 1952 detection of
technetium in red giants helped to prove that stars can produce heavier
elements.
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