Applications
Gadolinium has no large-scale applications but has a variety of specialized uses.
Gadolinium has the highest neutron cross-section among any stable nuclides: 61,000 barns for 155Gd and 259,000 barns for 157Gd. 157Gd has been used to target tumors in neutron therapy. This element is very effective for use with neutron radiography and in shielding of nuclear reactors. It is used as a secondary, emergency shut-down measure in some nuclear reactors, particularly of the CANDU type. Gadolinium is also used in nuclear marine propulsion systems as a burnable poison.
Gadolinium also possesses unusual metallurgic properties, with as little as 1% of gadolinium improving the workability and resistance of iron, chromium, and related alloys to high temperatures and oxidation.
Gadolinium is paramagnetic at room temperature, with a ferromagnetic Curie point of 20 °C. Paramagnetic ions, such as gadolinium, move differently within a magnetic field. This trait makes gadolinium useful for magnetic resonance imaging (MRI). Solutions of organic gadolinium complexes and gadolinium compounds are used as intravenous MRI contrast agent to enhance images in medical magnetic resonance imaging and magnetic resonance angiography (MRA) procedures. Magnevist is the most widespread example. Nanotubes packed with gadolinium, dubbed "gadonanotubes," are 40 times more effective than this traditional gadolinium contrast agent. Once injected, gadolinium-based contrast agents accumulate in abnormal tissues of the brain and body. This accumulation provides a greater contrast between normal and abnormal tissues, allowing doctors to better locate uncommon cell growths and tumors.
Gadolinium as a phosphor is also used in other imaging. In X-ray systems, gadolinium is contained in the phosphor layer, suspended in a polymer matrix at the detector. Terbium-doped gadolinium oxysulfide (Gd2O2S: Tb) at the phosphor layer converts the X-rays released from the source into light. This material emits green light at 540 nm due to the presence of Tb3+, which is very useful for enhancing the imaging quality. The energy conversion of Gd is up to 20%, which means that one-fifth of the X-rays striking the phosphor layer can be converted into light photons. Gadolinium oxyorthosilicate (Gd2SiO5, GSO; usually doped by 0.1–1% of Ce) is a single crystal that is used as a scintillator in medical imaging such as positron emission tomography or for detecting neutrons.
Gadolinium compounds are also used for making green phosphors for colour TV tubes and compact discs.
Gadolinium-153 is produced in a nuclear reactor from elemental europium or enriched gadolinium targets. It has a half-life of 240±10 days and emits gamma radiation with strong peaks at 41 keV and 102 keV. It is used in many quality assurance applications, such as line sources and calibration phantoms, to ensure that nuclear medicine imaging systems operate correctly and produce useful images of radioisotope distribution inside the patient. It is also used as a gamma ray source in X-ray absorption measurements or in bone density gauges for osteoporosis screening, as well as in the Lixiscope portable X-ray imaging system.
Gadolinium is used for making gadolinium yttrium garnet (Gd:Y3Al5O12); it has microwave applications and is used in fabrication of various optical components and as substrate material for magneto–optical films.
Gadolinium Gallium Garnet (GGG, Gd3Ga5O12) was used for imitation diamonds and for computer bubble memory.
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