Gadolinium is a
chemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
that has the symbol
Gd and
atomic numberIn chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
64. It is a silvery-white, malleable and ductile
rare-earthAs defined by IUPAC, rare earth elements or rare earth metals are a collection of seventeen chemical elements in the periodic table, namely scandium, yttrium, and the fifteen lanthanoids...
metal. Gadolinium has exceptionally high absorption of
neutronThe neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutron are usually found in atomic nuclei. The nuclei of most atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of protons in a...
s and therefore is used for shielding in neutron radiography and in nuclear reactors. Because of its
paramagneticParamagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability of ≥1 .The magnetic moment induced by the applied field is linear in the field...
properties, solutions of
organicOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
gadolinium
complexIn chemistry, a coordination complex or metal complex, is a structure consisting of a central atom or ion , bonded to a surrounding array of molecules or anions ....
es and gadolinium compounds are the most popular intravenous
MRI contrast agentMRI contrast agents are a group of contrast media used to improve the visibility of internal body structures in Magnetic resonance imaging . The most commonly used compounds for contrast enhancement are gadolinium-based...
s in medical magnetic resonance imaging.
Physical
Gadolinium is a silvery-white malleable and ductile
rare-earthAs defined by IUPAC, rare earth elements or rare earth metals are a collection of seventeen chemical elements in the periodic table, namely scandium, yttrium, and the fifteen lanthanoids...
metal. It crystallizes in
hexagonIn geometry, a hexagon is a polygon with six edges and six vertices. A regular hexagon has Schläfli symbol {6}.- Regular hexagon :The internal angles of a regular hexagon are all 120° and the hexagon has 720 degrees T. It has 6 rotational symmetries and 6 reflection symmetries, making up the...
al, close-packed alpha form at room temperature, but, when heated to temperatures above 1235 °C, it transforms into its beta form, which has a body-centered cubic structure.
Gadolinium-157 has the highest thermal neutron
captureNeutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than charged particles which are repelled by electrostatic...
cross-section of any known nuclide with the exception of
xenon-135135Xe is an unstable isotope of xenon with a half-lifeabout 9.2 hours. 135Xe is a fission product of Uranium which is the most powerful known neutron-absorbingnuclear poison and has a significant effect on...
, 49,000
barnsA barn is a unit of area. Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is used in all fields of high energy physics to express the cross sections of any scattering process...
, but it also has a fast burn-out rate, limiting its usefulness as a nuclear
control rodA control rod is a rod made of chemical elements capable of absorbing many neutrons without fissioning themselves. They are used in nuclear reactors to control the rate of fission of uranium and plutonium...
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
alloyAn alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history...
Gd
5(
SiSilicon is the most common metalloid. It is a chemical element, which has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon...
2GeGermanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. Germanium has five naturally occurring isotopes ranging in atomic mass number from 70 to 76...
2)
.
Individual gadolinium atoms have been isolated by encapsulating them into
fullereneA fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and cylindrical ones are called carbon nanotubes or buckytubes...
molecules and visualized with transmission electron microscope.. Individual Gd atoms and small Gd clusters have also been incorporated into carbon nanotubes.
Chemical
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.
- 4 Gd + 3 O2 → 2 Gd2O3
Gadolinium is a strong reducing agent, which reduces oxides of several metals, such as Fe, Cr, Sn, Pb, Mn and Zr, into their elements. Gadolinium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form gadolinium hydroxide:
- 2 Gd (s) + 6 H2O (l) → 2 Gd(OH)3 (aq) + 3 H2 (g)
Gadolinium metal reacts with all the halogens at temperature about 200 °C:
- 2 Gd (s) + 3 F2 (g) → 2 GdF3 (s) [white]
- 2 Gd (s) + 3 Cl2 (g) → 2 GdCl3 (s) [white]
- 2 Gd (s) + 3 Br2 (g) → 2 GdBr3 (s) [white]
- 2 Gd (s) + 3 I2 (g) → 2 GdI3 (s) [yellow]
Gadolinium dissolves readily in dilute sulphuric acid to form solutions containing the colorless Gd(III) ions, which exist as a [Gd(OH
2)
9]
3+ complexes:
- 2 Gd (s) + 3 H2SO4 (aq) → 2 Gd3+ (aq) + 3 (aq) + 3 H2 (g)
Gadolinium combines with nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic at elevated temperatures, forming binary compounds. In those compounds, Gd mostly exhibit oxidation state +3. Gadolinium(II) halides are obtained by annealing Gd(III) halides in presence of metallic Gd in tantalum containers. Gadolinium also form sesquichloride Gd
2Cl
3, which can be further reduced to GdCl by annealing at 800 °C. This gadolinium(I) chloride forms platelets with layered graphite-like structure.
Compounds
Compounds of gadolinium include:
- Fluoride
Fluoride is the anion F
−, the reduced form of fluorine. Both organic and inorganic compounds containing the element fluorine are sometimes called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are distinct relative to other...
s: GdF3
- Chloride
The chloride ion is formed when the element chlorine picks up one electron to form an anion Cl
−...
s: GdCl3Gadolinium chloride, also known as gadolinium trichloride, is GdCl
3. It is a colorless, hygroscopic, water-soluble solid. The hexahydrate GdCl
3∙6H
2O is commonly encountered and is sometimes also called gadolinium trichloride...
- Bromide
A bromide ion is a bromine atom with charge of −1.Compounds with bromine in formal oxidation state −1 are called bromides, and each individual chemical in this class can be called a bromide, as well...
s: GdBr3
- Nitrate
In inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms . In organic chemistry the esters of nitric acid and various alcohols are called nitrates.-Chemical properties:...
s: Gd(NO3)3Gadolinium nitrate is an inorganic compound of gadolinium. It is used as a water-soluble neutron poison in nuclear reactors.-Use:Gadolinium nitrate was used at the Savannah River Site heavy water nuclear reactors and has to be separated from the heavy water for storage or reuse...
- Iodide
An iodide ion is an iodine atom with a −1 charge. Compounds with iodine in formal oxidation state −1 are called iodides. This can include ionic compounds such as caesium iodide or covalent compounds such as phosphorus triiodide. This is the same naming scheme as is seen with chlorides...
s: GdI3
- Oxide
An oxide is a chemical compound containing at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon...
s: Gd2O3Gadolinium oxide is a chemical compound.Gadolinium oxide has two most common structures: Monoclinic and cubic . The cubic structure is similar to that of manganese oxide.-References:* Wells A.F...
- Sulfide
A sulfide is a chemical compound containing sulfur in its lowest oxidation number of −2.- Properties :...
s: Gd2S3
- Nitride
In chemistry, a nitride is a compound of nitrogen with a less electronegative element where nitrogen has an oxidation state of −3. Nitrides are a large class of compounds with a wide range of properties and applications....
s: GdN
- Organics
An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
: gadodiamideGadodiamide is a gadolinium-based contrast agent used in MR imaging procedures to assist in the visualization of blood vessels. It is commonly marketed under the trade name Omniscan.- Uses :...
Isotopes
Naturally occurring gadolinium is composed of 6 stable
isotopeIsotopes are different types of atoms of the same chemical element, each having a different number of neutrons. Correspondingly, isotopes differ in mass number but not in atomic number. The difference in the number of nucleons comes from a difference how many neutrons are in the atomic nucleus...
s,
154Gd,
155Gd,
156Gd,
157Gd,
158Gd and
160Gd, and 1 radioisotope,
152Gd, with
158Gd being the most abundant (24.84%
natural abundanceIn chemistry, natural abundance refers to the abundance isotopes of a chemical element as naturally found on a planet. The relative atomic mass of these isotopes is the atomic weight listed for the element in the periodic table...
). The predicted double beta decay of
160Gd has never been observed (only lower limit on its
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
of more than 1.3×10
21 years has been set experimentally ).
Twenty nine radioisotopes have been characterized, with the most stable being alpha-decaying
152Gd (naturally occurring) with a half-life of 1.08×10
14 years, and
150Gd with a half-life of 1.79×10
6 years. All of the remaining radioactive isotopes have half-lives less than 74.7 years. The majority of these have half-lives less than 24.6 seconds. Gadolinium isotopes have 4 metastable
isomerA nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons. A nuclear isomer occupies a higher energy state than the corresponding non-excited nucleus, called the ground state. Most nuclear excited states decay by gamma ray emission or...
s, with the most stable being
143mGd (
T½=110 seconds),
145mGd (
T½=85 seconds) and
141mGd (
T½=24.5 seconds).
The primary decay mode at
atomic massThe atomic mass is the mass of an atom, most often expressed in unified atomic mass units. The atomic mass may be considered to be the total mass of protons, neutrons and electrons in a single atom...
es lower than the most abundant stable isotope,
158Gd, is
electron captureElectron capture is a decay mode for isotopes that will occur when there are too many protons in the nucleus of an atom and insufficient energy to emit a positron; however, it continues to be a viable decay mode for radioactive isotopes that can decay by positron emission...
, and the primary mode at higher atomic masses is
beta decayIn nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
. The primary
decay productIn nuclear physics, a decay product is a nuclide produced by radioactive decay. Radioactive decay often involves a sequence of steps...
s for isotopes of weights lower than
158Gd are the element Eu (
europiumEuropium is a chemical element with the symbol Eu and atomic number 63. It was named after the continent of Europe.-Physical:Europium is about as hard as lead and quite ductile...
) isotopes and the primary products at higher weights are the element Tb (
terbiumTerbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...
) isotopes.
History
In 1880,
SwissSwitzerland , officially the Swiss Confederation , is a federal republic consisting of 26 states named cantons, with Bern as the seat of the federal authorities...
chemistA chemist is a scientist trained in the science of chemistry. Chemists study the composition of matter and its properties such as density, acidity, size and shape. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component...
Jean Charles Galissard de MarignacJean Charles Galissard de Marignac was a Swiss chemist whose work with atomic weights suggested the possibility of isotopes and the packing fraction of nuclei and whose study of the rare earth elements led to his discovery of ytterbium in 1878 and codiscovery of gadolinium in 1880.- Life and work...
observed spectroscopic lines due to gadolinium in samples of
didymiumDidymium is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially when a gas powered forge is used, where it provides a filter which blocks the yellowish light emitted by the hot sodium in the glass, without having a...
and
gadoliniteGadolinite is a mineral of a nearly black color and vitreous luster, and consisting principally of the silicates of cerium, lanthanum, neodymium, yttrium, beryllium, and iron with formula: 2FeBe2Si2O10...
;
FrenchFrance , officially the French Republic , is a country located in Western Europe, with several overseas islands and territories located on other continents. Metropolitan France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean...
chemist
Paul Émile Lecoq de BoisbaudranPaul Émile Lecoq de Boisbaudran was a French chemist born in Cognac. In 1858 he joined the family winemaking business, but a year later was working as a chemist....
separated
gadoliniaGadolinium oxide is a chemical compound.Gadolinium oxide has two most common structures: Monoclinic and cubic . The cubic structure is similar to that of manganese oxide.-References:* Wells A.F...
, 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
FinnishFinland , officially the Republic of Finland
, is a Nordic country and democracy situated in the Fennoscandian region of northern Europe. It borders Sweden on the west, Russia on the east, and Norway on the north, while Estonia lies to its south across the Gulf of Finland...
chemist and
geologistFor other uses, see Geologist .A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth and terrestrial planets...
Johan GadolinJohan Gadolin was a Finnish chemist, physicist and mineralogist. Gadolin discovered the chemical element yttrium...
. In older literature, the natural form of the element is often called an
earth, meaning that the element came from Earth.
Occurrence
Gadolinium is never found in nature as the free element, but is contained in many rare minerals such as
monaziteMonazite is a reddish-brown phosphate mineral containing rare earth metals and is an important source of thorium, lanthanum, and cerium. It occurs usually in small isolated crystals...
and
bastnäsiteThe mineral bastnäsite is one of a family of three carbonate-fluoride minerals. There is bastnäsite- with a formula of CO3F. There is bastnäsite- with a formula of CO3F. There is also bastnäsite- with a formula of CO3F...
. It occurs only in trace amounts in the mineral
gadoliniteGadolinite is a mineral of a nearly black color and vitreous luster, and consisting principally of the silicates of cerium, lanthanum, neodymium, yttrium, beryllium, and iron with formula: 2FeBe2Si2O10...
, which was also named after
Johan GadolinJohan Gadolin was a Finnish chemist, physicist and mineralogist. Gadolin discovered the chemical element yttrium...
. The abundance in the earth crust is about 6.2 mg/kg.
Production
Gadolinium is produced both from
monaziteMonazite is a reddish-brown phosphate mineral containing rare earth metals and is an important source of thorium, lanthanum, and cerium. It occurs usually in small isolated crystals...
and
bastnäsiteThe mineral bastnäsite is one of a family of three carbonate-fluoride minerals. There is bastnäsite- with a formula of CO3F. There is bastnäsite- with a formula of CO3F. There is also bastnäsite- with a formula of CO3F...
. Crushed minerals are attacked by hydrochloric or
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
that transforms insoluble rare-earth oxides into soluble chlorides or sulfates. The acidic filtrates are partially neutralized with caustic soda to pH 3-4.
ThoriumThorium is a chemical element with the symbol Th and atomic number 90. It is a naturally occurring, slightly radioactive metal. Thorium is estimated to be about three to four times more abundant than uranium in the earth's crust...
precipitates out of solution as hydroxide and is removed. After that the solution is treated with ammonium oxalate to convert rare earths in to their insoluble oxalates. The oxalates are converted to oxides by annealing. The oxides are dissolved in
nitric acidNitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure older samples tend to acquire a stronger yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as...
that excludes one of the main components,
ceriumCerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is...
, whose oxide is insoluble in HNO
3. The solution is treated with
magnesium nitrateMagnesium nitrate is a hygroscopic salt with the formula Mg2. In air, it quickly forms the hexahydrate with the formula Mg2·6H2O . It is very soluble in both water and ethanol.-Uses:Magnesium nitrate occurs in mines and caverns as nitromagnesite...
to produce a crystallized mixture of double salts of gadolinium,
samariumSamarium is a chemical element with the symbol Sm and atomic number 62.-Physical:Samarium is a rare earth metal, with a bright silver luster. Three crystal modifications of the metal also exist, with transformations at 734 and 922 °C, making it polymorphic...
and
europiumEuropium is a chemical element with the symbol Eu and atomic number 63. It was named after the continent of Europe.-Physical:Europium is about as hard as lead and quite ductile...
. The salts are separated by
ion exchangeIon exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
. In this process, rare-earth ions are sorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agent.
Gadolinium metal is obtained from its oxide or salts by heating with
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
at 1450 °C under argon atmosphere. Sponge gadolinium can be produced by reducing molten GdCl
3 with an appropriate metal oxide at temperatures below 1312 °C (melting point of Gd) in a reduced pressure.
Applications
Because of extremely high neutron cross-section of gadolinium, 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
CANDUThe CANDU reactor is a Canadian-invented, pressurized heavy water reactor developed initially in the late 1950s and 1960s by a partnership between Atomic Energy of Canada Limited , the Hydro-Electric Power Commission of Ontario , Canadian General Electric , as well as...
type. Gadolinium is also used in
nuclear marine propulsionNuclear marine propulsion is propulsion of a ship powered by a nuclear reactor. Naval nuclear propulsion is propulsion that specifically refers to naval warships .-Power plants:...
systems as a burnable poison.
Gadolinium is an efficient catalyst used for
decarboxylationDecarboxylation is any chemical reaction in which a carboxyl group is split off from a compound as carbon dioxide .- Common examples :Common biosynthetic decarboxylations of amino acids to amines are:* tryptophan to tryptamine...
of
oxaloacetic acidOxaloacetic acid is an organic compound with the chemical formula HO
2CCCH
2CO
2H. It also has other names and its conjugate base is called "oxaloacetate."-Function:...
, convertion of orto- to para-hydrogen and
polymerizationIn polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
of
ethyleneEthylene is the chemical compound with the formula C
2H
4. It is the simplest alkene. Because it contains a carbon-carbon double bond, ethylene is called an unsaturated hydrocarbon or an olefin. It is extremely important in industry and also has a role in biology as a hormone...
.
Gadolinium also possesses unusual
metallurgicMetallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
properties, with as little as 1% of gadolinium improving the workability and resistance of
ironIron is a metallic chemical element with the symbol Fe and atomic number 26. Iron is a group 8 and period 4 element and is therefore classified as a transition metal. Iron and iron alloys are by far the most common metals and the most common ferromagnetic materials in everyday use...
,
chromiumChromium is a chemical element which has the symbol Cr and atomic number 24, first element in Group 6. It is a steely-gray, lustrous, hard metal that takes a high polish and has a high melting point. It is also odourless, tasteless, and malleable...
, and related
alloyAn alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history...
s to high temperatures and oxidation. Magnesium alloy Elektron21 produced by Magnesium Elektron is a high strength magnesium alloy that uses gadolinium and neodymium as strengthening additions.
Because of their paramagnetic properties, solutions of
organicOrganic chemistry is a discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation of chemical compounds that contain carbon...
gadolinium
complexIn chemistry, a coordination complex or metal complex, is a structure consisting of a central atom or ion , bonded to a surrounding array of molecules or anions ....
es and gadolinium compounds are used as intravenous
MRI contrast agentMRI contrast agents are a group of contrast media used to improve the visibility of internal body structures in Magnetic resonance imaging . The most commonly used compounds for contrast enhancement are gadolinium-based...
to enhance images in medical magnetic resonance imaging. Magnevist is the most widespread example.
Beside MRI, gadolinium is also used in other imaging. In
X-rayX-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays...
, gadolinium is contained in the phosphor layer, suspending in a polymer matrix at the detector.
TerbiumTerbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife...
-doped
gadolinium oxysulfideGadolinium oxysulfide , also called gadolinium sulfoxylate or GOS, is an inorganic compound, a mixed oxide-sulfide of gadolinium. Its CAS number is ....
(Gd
2O
2S: Tb) at the phosphor layer is to convert the X-rays releasing from the source into light. This material emits green light at 540 nm due to the presence of Tb
3+, which is very useful for enhancing the imaging quality of the
X-rayX-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays...
that is exposed to the photographic film. The energy conversion of Gd is up to 20%, which means, one-fifth of the X-ray striking on the phosphor layer can be converted into light photons. Gadolinium oxyorthosilicate (Gd
2SiO
5, GSO; usually doped by 0.1-1% of
CeCerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight. It is...
) is a single crystal that is used as a
scintillatorA scintillator is material which exhibits the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e. reemit the absorbed energy in the form of a small flash of light, typically in the visible...
in medical imaging such as
positron emission tomographyPositron emission tomography is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
or for detecting neutrons.
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
osteoporosisOsteoporosis is a disease of bone that leads to an increased risk of fracture. In osteoporosis the bone mineral density is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered...
screening, as well as in the Lixiscope portable X-ray imaging system.
Gadolinium is used for making
gadolinium yttrium garnetGadolinium Yttrium Garnet is a variation of Nd:YAG with microwave and laser applications....
(Gd
3Ga
5O
12); it has
microwaveMicrowaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300MHz and 300 GHz. This is an extremely broad definition including both UHF and EHF , and various sources use different boundaries...
applications and is used in fabrication of various optical components and as substrate material for magneto–optical films. Gadolinium compounds are also used for making
phosphorA phosphor is a substance that exhibits the phenomenon of phosphorescence ....
s for colour
TVTelevision is a widely used telecommunication medium for transmitting and receiving moving images, either monochromatic or color, usually accompanied by sound. "Television" may also refer specifically to a television set, television programming or television transmission...
tubes,
compact discA Compact Disc is an optical disc used to store digital data. It was originally developed to store sound recordings exclusively, but later it also allowed the preservation of other types of data. Audio CDs have been commercially available since October 1982...
s and
computer memoryComputer memory refers to devices that are used to store data or programs on a temporary or permanent basis for use in an electronic digital computer. Computers represent information in binary code, written as sequences of 0s and 1s...
.
Biological role
Gadolinium has no known native biological role, but in research on biological systems it has a few roles. It is used as a component of MRI contrast agents, as, in the 3+ oxidation state, the metal has 7 unpaired f electrons. This causes water around the contrast agent to
relaxIn nuclear magnetic resonance spectroscopy and magnetic resonance imaging the term relaxation describes several processes by which nuclear magnetization prepared in a non-equilibrium state return to the equilibrium distribution. In other words, relaxation describes how fast spins "forget" the...
quickly, enhancing the quality of the MRI scan. Second, as a member of the lanthanides, it is used in various
ion channelIon channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of all living cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...
electrophysiology experiments, where it is used to block sodium leak channels, as well as to stretch activated ion channels.
Safety
As a free ion, gadolinium is highly toxic but is generally regarded as safe when administered as a
chelatedChelation is the formation or presence of two or more separate bindings between apolydentate ligand and a single central atom.Usually these ligands are organic compounds, and are called chelants, chelators, chelating agents, or sequestering agents....
compound. The compounds can be classified by whether they are macro-cyclic or linear
geometryMolecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.- Molecular geometry determination...
and whether they are ionic or not. Cyclical ionic Gd compounds being considered the least likely to release the Gd ion and hence the most safe. US Food and Drug Administration approved Gd chelated contrast agents include: Omniscan, Multihance, Magnevist,
ProHanceGadoteridol is a magnetic resonance contrast agent, used particularly in the imaging of the central nervous system. It is sold under the brand name ProHance....
, Vasovist and
OptiMARKGadoversetamide is a gadolinium compound used as a contrast agent in magnetic resonance imaging , particularly imaging of the brain, spine and liver. It is marketed under the trade name OptiMARK....
.
Gadolinium MRI contrast agents have proved safer than the iodinated contrast agents used in X-ray radiography or
computed tomographyComputed tomography is a medical imaging method employing tomography created by computer processing. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation.CT...
. Anaphylactoid reactions are rare, occurring in approx. 0.03-0.1%.
Although gadolinium agents have proved useful for patients with renal impairment, in patients with severe renal failure requiring dialysis there is a risk of a rare but serious illnesses, such as
nephrogenic systemic fibrosisNephrogenic systemic fibrosis or nephrogenic fibrosing dermopathy is a rare and serious syndrome that involves fibrosis of skin, joints, eyes, and internal organs. Its cause is not fully understood, but it seems to be associated with exposure to gadolinium in patients with severe kidney failure...
and nephrogenic fibrosing dermopathy, that may be linked to the use of certain gadolinium-containing agents. Although a causal link has not been definitively established, current guidelines in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
are that dialysis patients should only receive gadolinium agents where essential, and that
dialysisIn medicine, dialysis is primarily used to provide an artificial replacement for lost kidney function due to renal failure...
should be performed as soon as possible after the scan is complete, in order to remove the agent from the body promptly.
External links