Gadolinium Traditional Geocache

Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. Gadolinium has exceptionally high absorption of neutrons and therefore is used for shielding in neutron radiography and in nuclear reactors. Because of its paramagnetic properties, solutions of organic gadolinium complexes and gadolinium compounds are the most popular intravenous MRI contrast agents in medical magnetic resonance imaging.

Gadolinium is a silvery-white malleable and ductile rare-earth metal. It crystallizes in hexagonal, close-packed a- form at room temperature, but, when heated to temperatures above 1235 °C, it transforms into its ß- form, which has a body-centered cubic structure. Gadolinium-157 has the highest thermal neutron capture cross-section among any stable nuclides: 259,000 barns. Only xenon-135 has a higher cross section, 2 million barns, but that isotope is unstable. Gadolinium is strongly paramagnetic at room temperature, and exhibits ferromagnetic properties below room temperature. Gadolinium demonstrates a magnetocaloric effect whereby its temperature increases when it enters a magnetic field and decreases when it leaves the magnetic field. The effect is considerably stronger for the gadolinium alloy Gd₅(Si₂Ge₂). Individual gadolinium atoms have been isolated by encapsulating them into fullerene molecules and visualized with transmission electron microscope. Individual Gd atoms and small Gd clusters have also been incorporated into carbon nanotubes.

In 1880, Swiss chemist Jean Charles Galissard de Marignac observed spectroscopic lines due to gadolinium in samples of didymium and gadolinite; French chemist Paul Émile Lecoq de Boisbaudran separated gadolinia, the oxide of gadolinium, from Mosander's yttria in 1886. The element itself was isolated only recently. Gadolinium, like the mineral gadolinite, is named after Finnish chemist and geologist Johan Gadolin.

Gadolinium is a constituent in many minerals such as monazite and bastnäsite, which are oxides. The metal is too reactive to exist naturally. Ironically, the mineral gadolinite contains only traces of Gd. The abundance in the earth crust is about 6.2 mg/kg. The main mining areas are China, USA, Brazil, Sri Lanka, India and Australia with reserves expected to exceed one million tonnes. World production of pure gadolinium is about 400 tonnes per year.