Gadolinium Information
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Gadolinium Element
Gadolinium is a chemical
element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white
metal when oxidation is removed. It is only slightly malleable and is a ductile
rare-earth element. Gadolinium reacts with atmospheric oxygen or moisture
slowly to form a black coating. Gadolinium below its Curie point of 20 °C (68
°F) is ferromagnetic, with an attraction to a magnetic field higher than that
of nickel. Above this temperature it is the most paramagnetic element. It is
found in nature only in an oxidized form. When separated, it usually has
impurities of the other rare-earths because of their similar chemical properties.
Gadolinium was discovered in
1880 by Jean Charles de Marignac, who detected its oxide by using spectroscopy.
It is named after the mineral gadolinite, one of the minerals in which
gadolinium is found, itself named for the chemist Johan Gadolin. Pure
gadolinium was first isolated by the chemist Paul Emile Lecoq de Boisbaudran
around 1886.
In nature the element occurs as
a mixture of six stable isotopes—gadolinium-158 (24.84 percent), gadolinium-160
(21.86 percent), gadolinium-156 (20.47 percent), gadolinium-157 (15.65
percent), gadolinium-155 (14.8 percent), and gadolinium-154 (2.18 percent)—and
one radioactive isotope, gadolinium-152 (0.20 percent). Odd-numbered isotopes
have extremely high nuclear absorption cross sections, with that of
gadolinium-157 reaching 259,000 barns. As a result, the naturally occurring
mixture of gadolinium isotopes also has a very high nuclear absorption cross
section on the order of 49,000 barns. Excluding nuclear isomers, a total of 32
radioactive isotopes of gadolinium ranging in mass from 133 to 169 and having
half-lives from 1.1 seconds (gadolinium-135) to 1.08 × 1014 years
(gadolinium-152) have been characterized.
Gadolinium possesses unusual
metallurgical properties, to the extent that as little as 1% of gadolinium can
significantly improve the workability and resistance to oxidation at high
temperatures of iron, chromium, and related metals. Gadolinium as a metal or a
salt absorbs neutrons and is, therefore, used sometimes for shielding in
neutron radiography and in nuclear reactors.
Like most of the rare earths,
gadolinium forms trivalent ions with fluorescent properties, and salts of
gadolinium(III) are used as phosphors in various applications.
The kinds of gadolinium(III)
ions occurring in water-soluble salts are toxic to mammals. However, chelated
gadolinium(III) compounds are far less toxic because they carry gadolinium(III)
through the kidneys and out of the body before the free ion can be released
into the tissues. Because of its paramagnetic properties, solutions of chelated
organic gadolinium complexes are used as intravenously administered
gadolinium-based MRI contrast agents in medical magnetic resonance imaging.
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