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For radiation source for medical research.
(Gr. technetos, artificial) 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.
Twenty-two isotopes of technetium with masses ranging from 90 to 111 are reported. All
the isotopes of technetium are radioactive. It is one of two elements with Z < 83 that
have no stable isotopes; the other element is promethium (Z = 61). Technetium has three
long lived radioactive isotopes: 97Tc (T1/2
=2.6 x 106 years), 98Tc (T1/2
= 4.2 x 106 years) and 99Tc (T1/2
= 2.1 x 105 years). 95Tcm
("m" stands for meta state) (T1/2 = 61 days) is used in
tracer work. However, the most useful isotope of technetium is 99Tcm (T1/2 = 6.01 hours) is used in many medical
radioactive isotope tests because of its half-life being short, the energy of the gamma
ray it emits, and the ability of technetium to be chemically bound to many biologically
active molecules. Because 99Tc is produced as a fission product from
the fission of uranium in nuclear reactors, large quantities have been produced over the
years. There are kilogram quantities of technetium.
Technetium is a silvery-gray metal that tarnishes slowly in moist air. The common
oxidation states of technetium are +7, +5, and +4. Under oxidizing conditions technetium
(VII) will exist as the pertechnetate ion, TcO4-. The
chemistry of technetium is said to be similar to that of rhenium. Technetium dissolves in
nitric acid, aqua regia, and conc. sulfuric acid, but is not soluble in hydrochloric acid
of any strength. The element is a remarkable corrosion inhibitor for steel. The metal is
an excellent superconductor at 11K and below.
Until 1960, technetium was available only in small amounts and the price was as high as
$2800/g. It is now commercially available to holders of O.R.N.L. permits at a price of
It is reported that mild carbon steels may be effectively protected by as little as 55
ppm of KTcO4 in aerated distilled water at temperatures up to 250oC. This corrosion protection is limited to
closed systems, since technetium is radioative and must be confined. 98Tc
has a specific activity of 6.2 x 108
Bq/g. Activity of this level must not be allowed to spread. 99Tc
is a contamination hazard and should be handled in a glove box.
Sources: CRC Handbook of Chemistry
and Physics and the American Chemical Society.
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