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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 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 188; 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. Experiments at the
Facility for Rare Isotope Beams have reported lutetium-190 in
fragments of platinum-198 colliding with a carbon target.
The element also has 43 known nuclear isomers, of which the most
stable of them are lutetium-177m3, with a half-life of 160.4 days, and
lutetium-174m with a half-life of 142 days; longer than the ground
states of all lutetium isotopes except 173-176.
History
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Three scientists were involved in the discovery of lutetium: 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. Of the
three, Urbain was the first to publish, followed by Welsbach; James
was about to publish when he learned of Urbain's work, and thereafter
gave up his claim and did not publish. Despite staying out of the
priority argument, James worked on a much larger scale and possessed
the largest supply of lutetium at the time.
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.
Welsbach had achieved the separation before Urbain, but Urbain had
published 44 days earlier. Since Urbain was on the commission which
made the decision, its objectivity could be questioned and furthermore
Welsbach protested that Urbain's spectral evidence was weak and argued
that his rival's lutetium was very impure, but to no avail. After
Urbain's names were recognized, neoytterbium was reverted to
ytterbium.
The controversy died down after 1910, only to be reignited with the
discovery of element 72. Urbain claimed in 1911 to have discovered a
new rare earth named celtium and identified it as element 72. However,
Niels Bohr had demonstrated from his quantum theory that element 72
had to be a group 4 element and not a rare earth, and based on an idea
by Fritz Paneth, Bohr's friend George de Hevesy worked with Dirk
Coster to search for it in zirconium minerals. This they succeeded in
doing, discovering hafnium in 1923. This discovery announcement, being
in direct conflict with Urbain's celtium, ignited a controversy on
element 72 throughout the 1920s; the resulting investigations on the
nature of Urbain's celtium, since it was not the same as hafnium,
reopened the case on element 71. The physicists Hans M. Hansen and
Sven Werner, at Bohr's Copenhagen institute, found in 1923 that
Welsbach's 1907 samples of cassiopeium had been pure element 71, while
Urbain's 1907 lutecium samples only contained traces of element 71 and
his 1911 samples identified as celtium were actually pure element 71 -
confirming Welsbach's criticism. The Copenhagen physicists then
started a campaign to re-award priority for element 71 to Welsbach and
replace the name lutetium with cassiopeium, writing to Welsbach in
1923 of their intentions. This campaign encountered success in the
physics literature, but in spite of strong German and Scandinavian
support for cassiopeium, lutetium remained embedded in most of the
chemical literature, with the International Commission on Atomic
Weights in 1930 accepting that element 72 was hafnium but using
lutetium for element 71.
In 1949, it was decided by the International Union of Pure and Applied
Chemistry to recommend the name lutetium, since cassiopeium by then
was only used in German and sometimes Dutch, and it was a difficult
name to adapt to other languages; it was nonetheless clarified that
this was not intended as a statement on priority. Urbain's spelling
'lutecium' was changed to 'lutetium', in order to derive the name from
Latin 'Lutetia' instead of French 'Lutèce'. 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.
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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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There are few commercial uses specific to natural lutetium, and all of
them involve small quantities.
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
