Gadolinium is a chemical element that has the symbol Gd and atomic number 64.
Gadolinium is a silvery-white, malleable and ductile rare-earth metal with a metallic lustre. It crystallizes in hexagonal, close-packed alpha form at room temperature, but, when heated to 1508 K or more, it transforms into its beta form, which has a body-centered cubic structure.
Unlike other rare earth elements, gadolinium is relatively stable in dry air. However, it tarnishes quickly in moist air, forming a loosely-adhering oxide which spalls off, exposing more surface to oxidation. Gadolinium reacts slowly with water, and is soluble in dilute acids.
Gadolinium-157 has the highest thermal neutron capture cross-section of any known nuclide with the exception of xenon-135, 49,000 barns, but it also has a fast burn-out rate, limiting its usefulness as a nuclear control rod material.
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
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