Lutetium

Lutetium is a chemical element with the symbol Lu and atomic number 71. A metallic element, lutetium usually occurs in association with yttrium and is sometimes used in metal alloys and as a catalyst in various processes. A strict correlation between periodic table blocks and chemical series for neutral atoms would describe lutetium as a transition metal because it is in the d-block, but it is a lanthanide according to IUPAC.

Notable characteristics and applications
Lutetium is a silvery white corrosion-resistant trivalent metal that is relatively stable in air. Lutetium is the heaviest and hardest of the rare earth elements. Lutetium has the highest melting point of any lanthanide, probably related to the lanthanide contraction.

This element is very expensive to obtain in useful quantities and therefore it has very few commercial uses. However, stable lutetium can be used as catalysts in petroleum cracking in refineries and can also be used in alkylation, hydrogenation, and polymerization applications.

Lutetium-176 (176Lu) has been used to date the age of meteorites.

Lutetium aluminum garnet (Al5Lu3O12) has been proposed for use as a lens material in high refractive index immersion lithography.

Cerium-doped lutetium oxyorthosilicate (LSO) is currently the preferred compound for detectors in positron emission tomography (PET.)

History
Lutetium (Latin Lutetia meaning Paris) was independently discovered in 1907 by French scientist Georges Urbain, Austrian mineralogist Baron Carl Auer von Welsbach and American chemist Charles James. All men found lutetium as an impurity in the mineral ytterbia which was thought by Swiss chemist Jean Charles Galissard de Marignac (and most others) to consist entirely of the element ytterbium.

The separation of lutetium from Marignac's ytterbium was first described by Urbain and the naming honor therefore went to him. He chose the names neoytterbium (new ytterbium) and lutecium for the new element but neoytterbium was eventually reverted back to ytterbium and in 1949 the spelling of element 71 was changed to lutetium.

Welsbach proposed the names cassiopium for element 71 (after the constellation Cassiopeia) and aldebaranium for the new name of ytterbium but these naming proposals where rejected (although many German scientists in the 1950s called the element 71 cassiopium).

Occurrence
Found with almost all other rare-earth metals but never by itself, lutetium is very difficult to separate from other elements. Consequently, it is also one of the most expensive metals, costing about six times as much as gold.

The principal commercially viable ore of lutetium is the rare earth phosphate mineral monazite: (Ce, La, etc.) PO4 which contains 0.003% of the element. Pure lutetium metal has only relatively recently been isolated and is very difficult to prepare (thus it is one of the most rare and expensive of the rare earth metals). It is separated from other rare earth elements by ion exchange and then obtained in the elemental form by reduction of anhydrous LuCl3 or LuF3 by either an alkali metal or alkaline earth metal.

Isotopes
Naturally occurring lutetium is composed of 1 stable isotope Lu-175 (97.41% natural abundance). 33 radioisotopes have been characterized, with the most stable being Lu-176 with a half-life of 3.78 &times; 1010 years (2.59% natural abundance), Lu-174 with a half-life of 3.31 years, and Lu-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 a half an hour. This element also has 18 meta states, with the most stable being Lu-177m (t½ 160.4 days), Lu-174m (t½ 142 days) and Lu-178m (t½ 23.1 minutes).

The isotopes of lutetium range in atomic weight from 149.973 (Lu-150) to 183.961 (Lu-184). The primary decay mode before the most abundant stable isotope, Lu-175, is electron capture (with some alpha and positron emission), and the primary mode after is beta emission. The primary decay products before Lu-175 are element 70 (ytterbium) isotopes and the primary products after are element 72 (hafnium) isotopes.

Applications
Lutetium is very expensive (upwards of $100 per gram) to obtain on useful quantities and therefore it has very few commercial uses. Some commercial applications include:
 * Use as a pure beta emitter, using lutetium which has been exposed to neutron activation. A tiny amount of lutetium is added as a dopant to gadolinium gallium garnet (GGG), which is used in magnetic bubble memory devices.
 * Use as a catalyst in the petroleum industry, or in organic light-emitting diodes (OLEDs).
 * Research into possible uses for targeted radiotherapy for the development of new cancer therapies.

Compounds
Fluoride: LuF3, Chloride: LuCl3, Bromide: LuBr3, Iodide: LuI3, Oxide: Lu2O3, Sulfide: Lu2S3, Nitride: LuN

Intermetalic compounds:
 * Lutetium aluminum garnet

See also lutetium compounds.

Precautions
Like other rare-earth metals lutetium is regarded as having a low toxicity rating but it and especially its compounds should be handled with care nonetheless. Metal dust of this element is a fire and explosion hazard. Lutetium plays no biological role in the human body but is thought to help stimulate metabolism.