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History

Lutetium (Latin, Lutecia meaning Paris) was independently discovered in 1907-08 by French scientist Georges Urbain and Austrian mineralogist Baron Carl Auer von Welsbach.   Both 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 albebaranium for the new name of ytterbium but these naming proposals where rejected (although many German scientists in the 1950s called the element 71 cassiopium).

The refinement of ion exchange methods and their application to the separation of the rare-earths made the separation of lutetium from ytterbium possible. von Welsbach decided to rename ytterbium aldebaranium and picked cassiopium for element 71. Urbain preferred neoytterbium and lutecium. Urbain's choices eventually were accepted, although the prefix was dropped from ytterbium and the spelling of lutecium was eventually changed.

Characteristics

Lutetium is a silvery white corrosion-resistant trivalent metal that is relatively stable in air and is the heaviest and hardest of the rare earth elements.

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 craking in refineries and can also be used in alkylation, hydrogenation, and polymerization applications.

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 per gram 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.

Applications

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.)

Compounds

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 × 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-lifes that are less than 9 days, and the majority of these have half lifes that are less than a half an hour. This element also has 18 meta states, with the most stable being Lu-177m (t_½ 160.4 days), Lu-174m (t_½ 142 days) and Lu-178m (t_½ 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 ytterbium-70 isotopes and the primary products after are element hafnium-72 isotopes.

Precautions

Like other rare-earth metals lutetium is regarded as having a low toxcity 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.