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= Lutetium =
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Introduction
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Lutetium is a chemical element; it has symbol Lu and atomic number 71.
It is a silvery white metal, which resists corrosion in dry air, but
not in moist air. Lutetium is the last element in the lanthanide
series, and it is traditionally counted among the rare earth elements;
it can also be classified as the first element of the 6th-period
transition metals.
Lutetium was independently discovered in 1907 by French scientist
Georges Urbain, Austrian mineralogist Baron Carl Auer von Welsbach,
and American chemist Charles James. All of these researchers found
lutetium as an impurity in ytterbium. The dispute on the priority of
the discovery occurred shortly after, with Urbain and Welsbach
accusing each other of publishing results influenced by the published
research of the other; the naming honor went to Urbain, as he had
published his results earlier. He chose the name 'lutecium' for the
new element, but in 1949 the spelling was changed to 'lutetium'. In
1909, the priority was finally granted to Urbain and his names were
adopted as official ones; however, the name 'cassiopeium' (or later
'cassiopium') for element 71 proposed by Welsbach was used by many
German scientists until the 1950s.
Lutetium is not a particularly abundant element, although it is
significantly more common than silver in the Earth's crust. It has few
specific uses. Lutetium-176 is a relatively abundant (2.5%)
radioactive isotope with a half-life of about 38 billion years, used
to determine the age of minerals and meteorites. Lutetium usually
occurs in association with the element yttrium and is sometimes used
in metal alloys and as a catalyst in various chemical reactions.
177Lu-DOTA-TATE is used for radionuclide therapy (see Nuclear
medicine) on neuroendocrine tumours. Lutetium has the highest Brinell
hardness of any lanthanide, at 890-1300 MPa.
Physical properties
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A lutetium atom has 71 electrons, arranged in the configuration [Xe]
4f145d16s2. Lutetium is generally encountered in the +3 oxidation
state, having lost its two outermost 6s and the single 5d-electron.
The lutetium atom is the smallest among the lanthanide atoms, due to
the lanthanide contraction, and as a result lutetium has the highest
density, melting point, and hardness of the lanthanides. As lutetium's
4f orbitals are highly stabilized only the 5d and 6s orbitals are
involved in chemical reactions and bonding; thus it is characterized
as a d-block rather than an f-block element, and on this basis some
consider it not to be a lanthanide at all, but a transition metal like
its lighter congeners scandium and yttrium.
Chemical properties and compounds
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Lutetium's compounds almost always contain the element in the +3
oxidation state. Aqueous solutions of most lutetium salts are
colorless and form white crystalline solids upon drying, with the
common exception of the iodide, which is brown. The soluble salts,
such as nitrate, sulfate and acetate form hydrates upon
crystallization. The oxide, hydroxide, fluoride, carbonate, phosphate
and oxalate are insoluble in water.
Lutetium metal is slightly unstable in air at standard conditions, but
it burns readily at 150 °C to form lutetium oxide. The resulting
compound is known to absorb water and carbon dioxide, and it may be
used to remove vapors of these compounds from closed atmospheres.
Similar observations are made during reaction between lutetium and
water (slow when cold and fast when hot); lutetium hydroxide is formed
in the reaction. Lutetium metal is known to react with the four
lightest halogens to form trihalides; except the fluoride they are
soluble in water.
Lutetium dissolves readily in weak acids and dilute sulfuric acid to
form solutions containing the colorless lutetium ions, which are
coordinated by between seven and nine water molecules, the average
being .
:
Oxidation states
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Lutetium is usually found in the +3 oxidation state, like most other
lanthanides. However, it can also be in the 0, +1 and +2 states as
well.
Isotopes
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Lutetium occurs on the Earth in form of two isotopes: lutetium-175 and
lutetium-176. Out of these two, only the former is stable, making the
element monoisotopic. The latter one, lutetium-176, decays via beta
decay with a half-life of ; it makes up about 2.5% of natural
lutetium.
To date, 40 synthetic radioisotopes of the element have been
characterized, ranging in mass number from 149 to 190; the most stable
such isotopes are lutetium-174 with a half-life of 3.31 years, and
lutetium-173 with a half-life of 1.37 years. All of the remaining
radioactive isotopes have half-lives that are less than 9 days, and
the majority of these have half-lives that are less than half an hour.
Isotopes lighter than the stable lutetium-175 decay via electron
capture (to produce isotopes of ytterbium), with some alpha and
positron emission; the heavier isotopes decay primarily via beta
decay, producing hafnium isotopes.
The element also has 43 known nuclear isomers, with masses of 150,
151, 153-162, and 166-180 (not every mass number corresponds to only
one isomer). The most stable of them are lutetium-177m, with a
half-life of 160.4 days, and lutetium-174m, with a half-life of 142
days; these are longer than the half-lives of the ground states of all
radioactive lutetium isotopes except lutetium-173, 174, and 176.
History
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The discovery of lutetium was intertwined with that of ytterbium and
thulium. Three scientists were involved in all three elements: French
scientist Georges Urbain, Austrian mineralogist Baron Carl Auer von
Welsbach, and American chemist Charles James. They found lutetium as
an impurity in ytterbia, which was thought by Swiss chemist Jean
Charles Galissard de Marignac to consist entirely of ytterbium.
Urbain and Welsbach proposed different names. Urbain chose
'neoytterbium' for ytterbium and 'lutecium' for the new element.
Welsbach chose 'aldebaranium' and 'cassiopeium' (after Aldebaran and
Cassiopeia). Both authors accused the other man of publishing results
based on their work.
The International Commission on Atomic Weights, which was then
responsible for the attribution of new element names, settled the
dispute in 1909 by granting priority to Urbain and adopting his choice
for a name, one derived from the Latin 'Lutetia' (Paris). This
decision was based on the fact that the separation of lutetium from
Marignac's ytterbium was first described by Urbain; after Urbain's
names were recognized, neoytterbium was reverted to ytterbium.
The controversy did not end. Confusion over element 72, Zirconium lead
x-ray spectroscopic studies that suggested Welsbach's 1907 samples of
lutetium had been pure, while Urbain's 1907 samples only contained
traces of lutetium. Charles James, who stayed out of the priority
argument, worked on a much larger scale and possessed the largest
supply of lutetium at the time. Pure lutetium metal was first produced
in 1953.
Occurrence and production
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Monazite
Found with almost all other rare-earth metals but never by itself,
lutetium is very difficult to separate from other elements. Its
principal commercial source is as a by-product from the processing of
the rare earth phosphate mineral monazite (, which has concentrations
of only 0.0001% of the element, not much higher than the abundance of
lutetium in the Earth crust of about 0.5 mg/kg. No lutetium-dominant
minerals are currently known. The main mining areas are China,
United States, Brazil, India, Sri Lanka and Australia. The world
production of lutetium (in the form of oxide) is about 10 tonnes per
year. Pure lutetium metal is very difficult to prepare. It is one of
the rarest and most expensive of the rare earth metals with the price
about US$10,000 per kilogram, or about one-fourth that of gold.
Crushed minerals are treated with hot concentrated sulfuric acid to
produce water-soluble sulfates of rare earths. Thorium precipitates
out of solution as hydroxide and is removed. After that the solution
is treated with ammonium oxalate to convert rare earths into their
insoluble oxalates. The oxalates are converted to oxides by annealing.
The oxides are dissolved in nitric acid that excludes one of the main
components, cerium, whose oxide is insoluble in HNO3. Several rare
earth metals, including lutetium, are separated as a double salt with
ammonium nitrate by crystallization. Lutetium is separated by ion
exchange. In this process, rare-earth ions are adsorbed onto suitable
ion-exchange resin by exchange with hydrogen, ammonium or cupric ions
present in the resin. Lutetium salts are then selectively washed out
by suitable complexing agent. Lutetium metal is then obtained by
reduction of anhydrous LuCl3 or LuF3 by either an alkali metal or
alkaline earth metal.
:
177Lu is produced by neutron activation of 176Lu or by indirectly by
neutron activation of 176Yb followed by beta decay. The 6.693 day half
life allows transport from the production reactor to the point of use
without significant loss in activity.
Applications
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Small quantities of lutetium have many speciality uses.
Stable isotopes
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Stable lutetium can be used as catalysts in petroleum cracking in
refineries and can also be used in alkylation, hydrogenation, and
polymerization applications.
Lutetium aluminium garnet () has been proposed for use as a lens
material in high refractive index immersion lithography. Additionally,
a tiny amount of lutetium is added as a dopant to gadolinium gallium
garnet, which was used in magnetic bubble memory devices. Cerium-doped
lutetium oxyorthosilicate is currently the preferred compound for
detectors in positron emission tomography (PET). Lutetium aluminium
garnet (LuAG) is used as a phosphor in light-emitting diode light
bulbs.
Lutetium tantalate (LuTaO4) is the densest known stable white material
(density 9.81 g/cm3) and therefore is an ideal host for X-ray
phosphors. The only denser white material is thorium dioxide, with
density of 10 g/cm3, but the thorium it contains is radioactive.
Lutetium is also a compound of several scintillating materials, which
convert X-rays to visible light. It is part of LYSO, LuAG and lutetium
iodide scintillators.
Research indicates that lutetium-ion atomic clocks could provide
greater accuracy than any existing atomic clock.
Unstable isotopes
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The suitable half-life and decay mode made lutetium-176 used as a pure
beta emitter, using lutetium which has been exposed to neutron
activation, and in lutetium-hafnium dating to date meteorites.
The isotope 177Lu emits low-energy beta particles and gamma rays and
has a half-life around 7 days, positive characteristics for commercial
applications, especially in therapeutic nuclear medicine.
The synthetic isotope lutetium-177 bound to octreotate (a somatostatin
analogue), is used experimentally in targeted radionuclide therapy for
neuroendocrine tumors. Lutetium-177 is used as a radionuclide in
neuroendocrine tumor therapy and bone pain palliation.
Lutetium (177Lu) vipivotide tetraxetan is a therapy for prostate
cancer, FDA approved in 2022.
Precautions
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Like other rare-earth metals, lutetium is regarded as having a low
degree of toxicity, but its compounds should be handled with care
nonetheless: for example, lutetium fluoride inhalation is dangerous
and the compound irritates skin. Lutetium nitrate may be dangerous as
it may explode and burn once heated. Lutetium oxide powder is toxic as
well if inhaled or ingested.
Similarly to the other rare-earth metals, lutetium has no known
biological role, but it is found even in humans, concentrating in
bones, and to a lesser extent in the liver and kidneys. Lutetium salts
are known to occur together with other lanthanide salts in nature; the
element is the least abundant in the human body of all lanthanides.
Human diets have not been monitored for lutetium content, so it is not
known how much the average human takes in, but estimations show the
amount is only about several micrograms per year, all coming from tiny
amounts absorbed by plants. Soluble lutetium salts are mildly toxic,
but insoluble ones are not.
License
=========
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Original Article:
http://en.wikipedia.org/wiki/Lutetium
