Samarium

Template:Use American English Template:Infobox samarium Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samarium(II) are also known, most notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as well as samarium(II) iodide.

Discovered in 1879 by French chemist Paul-Émile Lecoq de Boisbaudran, samarium was named after the mineral samarskite from which it was isolated. The mineral itself was named after a Russian mine official, Colonel Vassili Samarsky-Bykhovets, who thus became the first person to have a chemical element named after him, though the name was indirect.

Samarium occurs in concentration up to 2.8% in several minerals including cerite, gadolinite, samarskite, monazite and bastnäsite, the last two being the most common commercial sources of the element. These minerals are mostly found in China, the United States, Brazil, India, Sri Lanka and Australia; China is by far the world leader in samarium mining and production.

The main commercial use of samarium is in samarium–cobalt magnets, which have permanent magnetization second only to neodymium magnets; however, samarium compounds can withstand significantly higher temperatures, above Template:Convert, without losing their permanent magnetic properties. The radioisotope samarium-153 is the active component of the drug samarium (¹⁵³Sm) lexidronam (Quadramet), which kills cancer cells in lung cancer, prostate cancer, breast cancer and osteosarcoma. Another isotope, samarium-149, is a strong neutron absorber and so is added to control rods of nuclear reactors. It also forms as a decay product during reactor operation and is one of the important factors considered in reactor design and operation. Other uses of samarium include catalysis of chemical reactions, radioactive dating and X-ray lasers. Samarium(II) iodide, in particular, is a common reducing agent in chemical synthesis.

Samarium has no biological role; some samarium salts are slightly toxic.

Physical properties

Samarium is a rare earth element with a hardness and density similar to zinc. With a boiling point of Template:Convert, samarium is the third most volatile lanthanide after ytterbium and europium and comparable in this respect to lead and barium; this helps separation of samarium from its ores. When freshly prepared, samarium has a silvery lustre, and takes on a duller appearance when oxidized in air. Samarium is calculated to have one of the largest atomic radii of the elements; with a radius of 238 pm, only potassium, praseodymium, barium, rubidium and caesium are larger.

In ambient conditions, samarium has a rhombohedral structure (α form). Upon heating to Template:Convert, its crystal symmetry changes to hexagonal close-packed (hcp),; it has actual transition temperature depending on metal purity. Further heating to Template:Convert transforms the metal into a body-centered cubic (bcc) phase. Heating to Template:Convert plus compression to 40 kbar results in a double-hexagonally close-packed structure (dhcp). Higher pressure of the order of hundreds or thousands of kilobars induces a series of phase transformations, in particular with a tetragonal phase appearing at about 900 kbar. In one study, the dhcp phase could be produced without compression, using a nonequilibrium annealing regime with a rapid temperature change between about Template:Convert and Template:Convert, confirming the transient character of this samarium phase. Thin films of samarium obtained by vapor deposition may contain the hcp or dhcp phases in ambient conditions.

Samarium and its sesquioxide are paramagnetic at room temperature. Their corresponding effective magnetic moments, below 2 bohr magnetons, are the third-lowest among lanthanides (and their oxides) after lanthanum and lutetium. The metal transforms to an antiferromagnetic state upon cooling to 14.8 K. Individual samarium atoms can be isolated by encapsulating them into fullerene molecules. They can also be intercalated into the interstices of the bulk C₆₀ to form a solid solution of nominal composition Sm₃C₆₀, which is superconductive at a temperature of 8 K. Samarium doping of iron-based superconductors – a class of high-temperature superconductor – increases their transition to normal conductivity temperature up to 56 K, the highest value achieved so far in this series.

Chemical properties

In air, samarium slowly oxidizes at room temperature and spontaneously ignites at Template:Convert. Even when stored under mineral oil, samarium gradually oxidizes and develops a grayish-yellow powder of the oxide-hydroxide mixture at the surface. The metallic appearance of a sample can be preserved by sealing it under an inert gas such as argon.

Samarium is quite electropositive and reacts slowly with cold water and rapidly with hot water to form samarium hydroxide:

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Samarium dissolves readily in dilute sulfuric acid to form solutions containing the yellow to pale green Sm(III) ions, which exist as Template:Chem2 complexes:

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Samarium is one of the few lanthanides with a relatively accessible +2 oxidation state, alongside Eu and Yb. Template:Chem2 ions are blood-red in aqueous solution.

Compounds

Formula	Color	Symmetry	Space group	No.	Pearson symbol	a (pm)	b (pm)	c (pm)	Z	Density, g/cm3
Sm	silvery	trigonal	R3m	166	hR9	362.9	362.9	2621.3	9	7.52
Sm	silvery	hexagonal	P63/mmc	194	hP4	362	362	1168	4	7.54
Sm	silvery	tetragonal	I4/mmm	139	tI2	240.2	240.2	423.1	2	20.46
SmO	golden	cubic	Fm3m	225	cF8	494.3	494.3	494.3	4	9.15
Sm2O3		trigonal	P3m1	164	hP5	377.8	377.8	594	1	7.89
Sm2O3		monoclinic	C2/m	12	mS30	1418	362.4	885.5	6	7.76
Sm2O3		cubic	Ia3	206	cI80	1093	1093	1093	16	7.1
SmH2		cubic	Fm3m	225	cF12	537.73	537.73	537.73	4	6.51
SmH3		hexagonal	P3c1	165	hP24	377.1	377.1	667.2	6
Sm2B5	gray	monoclinic	P21/c	14	mP28	717.9	718	720.5	4	6.49
SmB2		hexagonal	P6/mmm	191	hP3	331	331	401.9	1	7.49
SmB4		tetragonal	P4/mbm	127	tP20	717.9	717.9	406.7	4	6.14
SmB6		cubic	Pm3m	221	cP7	413.4	413.4	413.4	1	5.06
SmB66		cubic	Fm3c	226	cF1936	2348.7	2348.7	2348.7	24	2.66
Sm2C3		cubic	I43d	220	cI40	839.89	839.89	839.89	8	7.55
SmC2		tetragonal	I4/mmm	139	tI6	377	377	633.1	2	6.44
SmF2	purple	cubic	Fm3m	225	cF12	587.1	587.1	587.1	4	6.18
SmF3	white	orthorhombic	Pnma	62	oP16	667.22	705.85	440.43	4	6.64
SmCl2	brown	orthorhombic	Pnma	62	oP12	756.28	450.77	901.09	4	4.79
SmCl3	yellow	hexagonal	P63/m	176	hP8	737.33	737.33	416.84	2	4.35
SmBr2	brown	orthorhombic	Pnma	62	oP12	797.7	475.4	950.6	4	5.72
SmBr3	yellow	orthorhombic	Cmcm	63	oS16	404	1265	908	2	5.58
SmI2	green	monoclinic	P21/c	14	mP12
SmI3	orange	trigonal	R3	63	hR24	749	749	2080	6	5.24
SmN		cubic	Fm3m	225	cF8	357	357	357	4	8.48
SmP		cubic	Fm3m	225	cF8	576	576	576	4	6.3
SmAs		cubic	Fm3m	225	cF8	591.5	591.5	591.5	4	7.23

Oxides

The most stable oxide of samarium is the sesquioxide Sm₂O₃. Like many samarium compounds, it exists in several crystalline phases. The trigonal form is obtained by slow cooling from the melt. The melting point of Sm₂O₃ is high (2345 °C), so it is usually melted not by direct heating, but with induction heating, through a radio-frequency coil. Sm₂O₃ crystals of monoclinic symmetry can be grown by the flame fusion method (Verneuil process) from Sm₂O₃ powder, that yields cylindrical boules up to several centimeters long and about one centimeter in diameter. The boules are transparent when pure and defect-free and are orange otherwise. Heating the metastable trigonal Sm₂O₃ to Template:Convert converts it to the more stable monoclinic phase. Cubic Sm₂O₃ has also been described.

Samarium is one of the few lanthanides that form a monoxide, SmO. This lustrous golden-yellow compound was obtained by reducing Sm₂O₃ with samarium metal at high temperature (1000 °C) and a pressure above 50 kbar; lowering the pressure resulted in incomplete reaction. SmO has cubic rock-salt lattice structure.

Chalcogenides

Samarium forms a trivalent sulfide, selenide and telluride. Divalent chalcogenides SmS, SmSe and SmTe with a cubic rock-salt crystal structure are known. These chalcogenides convert from a semiconducting to metallic state at room temperature upon application of pressure. Whereas the transition is continuous and occurs at about 20–30 kbar in SmSe and SmTe, it is abrupt in SmS and requires only 6.5 kbar. This effect results in a spectacular color change in SmS from black to golden yellow when its crystals of films are scratched or polished. The transition does not change the lattice symmetry, but there is a sharp decrease (~15%) in the crystal volume. It exhibits hysteresis, i.e., when the pressure is released, SmS returns to the semiconducting state at a much lower pressure of about 0.4 kbar.

Halides

File:Samarium(III) chloride hexahydrate.jpg

Samarium trichloride

Samarium metal reacts with all the halogens, forming trihalides:

2 Sm (s) + 3 X₂ (g) → 2 SmX₃ (s) (X = F, Cl, Br or I)

Their further reduction with samarium, lithium or sodium metals at elevated temperatures (about 700–900 °C) yields the dihalides. The diiodide can also be prepared by heating SmI₃, or by reacting the metal with 1,2-diiodoethane in anhydrous tetrahydrofuran at room temperature:

Sm (s) + ICH₂-CH₂I → SmI₂ + CH₂=CH₂.

In addition to dihalides, the reduction also produces many non-stoichiometric samarium halides with a well-defined crystal structure, such as Sm₃F₇, Sm₁₄F₃₃, Sm₂₇F₆₄, Sm₁₁Br₂₄, Sm₅Br₁₁ and Sm₆Br₁₃.

Samarium halides change their crystal structures when one type of halide anion is substituted for another, which is an uncommon behavior for most elements (e.g. actinides). Many halides have two major crystal phases for one composition, one being significantly more stable and another being metastable. The latter is formed upon compression or heating, followed by quenching to ambient conditions. For example, compressing the usual monoclinic samarium diiodide and releasing the pressure results in a PbCl₂-type orthorhombic structure (density 5.90 g/cm³), and similar treatment results in a new phase of samarium triiodide (density 5.97 g/cm³).

Borides

Sintering powders of samarium oxide and boron, in a vacuum, yields a powder containing several samarium boride phases; the ratio between these phases can be controlled through the mixing proportion. The powder can be converted into larger crystals of samarium borides using arc melting or zone melting techniques, relying on the different melting/crystallization temperature of SmB₆ (2580 °C), SmB₄ (about 2300 °C) and SmB₆₆ (2150 °C). All these materials are hard, brittle, dark-gray solids with the hardness increasing with the boron content. Samarium diboride is too volatile to be produced with these methods and requires high pressure (about 65 kbar) and low temperatures between 1140 and 1240 °C to stabilize its growth. Increasing the temperature results in the preferential formation of SmB₆.

Samarium hexaboride

Samarium hexaboride is a typical intermediate-valence compound where samarium is present both as Sm²⁺ and Sm³⁺ ions in a 3:7 ratio. It belongs to a class of Kondo insulators; at temperatures above 50 K, its properties are typical of a Kondo metal, with metallic electrical conductivity characterized by strong electron scattering, whereas at lower temperatures, it behaves as a non-magnetic insulator with a narrow band gap of about 4–14 meV. The cooling-induced metal-insulator transition in SmB₆ is accompanied by a sharp increase in the thermal conductivity, peaking at about 15 K. The reason for this increase is that electrons themselves do not contribute to the thermal conductivity at low temperatures, which is dominated by phonons, but the decrease in electron concentration reduces the rate of electron-phonon scattering.

Other inorganic compounds

A tube of samarium sulfate

Samarium sulfate, Sm₂(SO₄)₃

Samarium carbides are prepared by melting a graphite-metal mixture in an inert atmosphere. After the synthesis, they are unstable in air and need to be studied under an inert atmosphere. Samarium monophosphide SmP is a semiconductor with a bandgap of 1.10 eV, the same as in silicon, and electrical conductivity of n-type. It can be prepared by annealing at Template:Convert an evacuated quartz ampoule containing mixed powders of phosphorus and samarium. Phosphorus is highly volatile at high temperatures and may explode, thus the heating rate has to be kept well below 1 °C/min. A similar procedure is adopted for the monarsenide SmAs, but the synthesis temperature is higher at Template:Convert.

Numerous crystalline binary compounds are known for samarium and one of the group 14, 15, or 16 elements X, where X is Si, Ge, Sn, Pb, Sb or Te, and metallic alloys of samarium form another large group. They are all prepared by annealing mixed powders of the corresponding elements. Many of the resulting compounds are non-stoichiometric and have nominal compositions Sm_aX_b, where the b/a ratio varies between 0.5 and 3.

Organometallic compounds

Samarium forms a cyclopentadienide Template:Chem2 and its chloroderivatives Template:Chem2 and Template:Chem2. They are prepared by reacting samarium trichloride with Template:Chem2 in tetrahydrofuran. Contrary to cyclopentadienides of most other lanthanides, in Template:Chem2 some Template:Chem2 rings bridge each other by forming ring vertexes η¹ or edges η² toward another neighboring samarium, thus creating polymeric chains. The chloroderivative Template:Chem2 has a dimer structure, which is more accurately expressed as Template:Chem2. There, the chlorine bridges can be replaced, for instance, by iodine, hydrogen or nitrogen atoms or by CN groups.

The (Template:Chem2)⁻ ion in samarium cyclopentadienides can be replaced by the indenide (Template:Chem2)⁻ or cyclooctatetraenide (Template:Chem2)²⁻ ring, resulting in Template:Chem2 or Template:Chem2. The latter compound has a structure similar to uranocene. There is also a cyclopentadienide of divalent samarium, Template:Chem2 a solid that sublimates at about Template:Convert. Contrary to ferrocene, the Template:Chem2 rings in Template:Chem2 are not parallel but are tilted by 40°.

A metathesis reaction in tetrahydrofuran or ether gives alkyls and aryls of samarium:

Template:Chem2

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Here R is a hydrocarbon group and Me = methyl.

Isotopes

Naturally occurring samarium is composed of five stable isotopes: ¹⁴⁴Sm, ¹⁴⁹Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and two extremely long-lived radioisotopes, ¹⁴⁷Sm (half-life t_1/2 = 1.06Template:E years) and ¹⁴⁸Sm (7Template:E years), with ¹⁵²Sm being the most abundant (26.75%).Template:NUBASE2020 ¹⁴⁹Sm is listed by various sources as being stable,Template:NUBASE2020 but some sources state that it is radioactive, with a lower bound for its half-life given as Template:Val years.Template:NUBASE2020 Some observationally stable samarium isotopes are predicted to decay to isotopes of neodymium. The long-lived isotopes ¹⁴⁶Sm, ¹⁴⁷Sm, and ¹⁴⁸Sm undergo alpha decay to neodymium isotopes. Lighter unstable isotopes of samarium mainly decay by electron capture to promethium, while heavier ones beta decay to europium.Template:NUBASE2020 The known isotopes range from ¹²⁹Sm to ¹⁶⁸Sm.Template:NUBASE2020 The half-lives of ¹⁵¹Sm and ¹⁴⁵Sm are 90 years and 340 days, respectively. All remaining radioisotopes have half-lives that are less than 2 days, and most these have half-life less than 48 seconds. Samarium also has twelve known nuclear isomers, the most stable of which are ^141mSm (half-life 22.6 minutes), ^143m1Sm (t_1/2 = 66 seconds), and ^139mSm (t_1/2 = 10.7 seconds).Template:NUBASE2020 Natural samarium has a radioactivity of 127 Bq/g, mostly due to ¹⁴⁷Sm, which alpha decays to ¹⁴³Nd with a half-life of 1.06Template:E years and is used in samarium–neodymium dating. ¹⁴⁶Sm is an extinct radionuclide, with the half-life of 9.20Template:E years. There have been searches of samarium-146 as a primordial nuclide, because its half-life is long enough such that minute quantities of the element should persist today. It can be used in radiometric dating.

Samarium-149 is an observationally stable isotope of samarium (predicted to decay, but no decays have ever been observed, giving it a half-life at least several orders of magnitude longer than the age of the universe), and a product of the decay chain from the fission product ¹⁴⁹Nd (yield 1.0888%). ¹⁴⁹Sm is a decay product and neutron-absorber in nuclear reactors, with a neutron poison effect that is second in importance for reactor design and operation only to ¹³⁵Xe. Its neutron cross section is 41000 barns for thermal neutrons. Because samarium-149 is not radioactive and is not removed by decay, it presents problems somewhat different from those encountered with xenon-135. The equilibrium concentration (and thus the poisoning effect) builds to an equilibrium value during reactor operations in about 500 hours (about three weeks), and since samarium-149 is stable, its concentration remains essentially constant during reactor operation.

Chemical structure of samarium (153Sm) lexidronam

Chemical structure of Sm-EDTMP

Samarium-153 is a beta emitter with a half-life of 46.3 hours. It is used to kill cancer cells in lung cancer, prostate cancer, breast cancer, and osteosarcoma. For this purpose, samarium-153 is chelated with ethylene diamine tetramethylene phosphonate (EDTMP) and injected intravenously. The chelation prevents accumulation of radioactive samarium in the body that would result in excessive irradiation and generation of new cancer cells. The corresponding drug has several names including samarium (¹⁵³Sm) lexidronam; its trade name is Quadramet.

History

Lecoq de Boisbaudran

Paul Émile Lecoq de Boisbaudran, the discoverer of samarium

Detection of samarium and related elements was announced by several scientists in the second half of the 19th century; however, most sources give priority to French chemist Paul-Émile Lecoq de Boisbaudran. Boisbaudran isolated samarium oxide and/or hydroxide in Paris in 1879 from the mineral samarskite Template:Chem2) and identified a new element in it via sharp optical absorption lines. Swiss chemist Marc Delafontaine announced a new element decipium (from Template:Langx meaning "deceptive, misleading") in 1878, but later in 1880–1881 demonstrated that it was a mix of several elements, one being identical to Boisbaudran's samarium. Though samarskite was first found in the Ural Mountains in Russia, by the late 1870s it had been found in other places, making it available to many researchers. In particular, it was found that the samarium isolated by Boisbaudran was also impure and had a comparable amount of europium. The pure samarium(III) oxide was produced only in 1901 by Eugène-Anatole Demarçay, and in 1903 Wilhelm Muthmann isolated the element.

Boisbaudran named his element samarium after the mineral samarskite, which in turn honored Vassili Samarsky-Bykhovets (1803–1870). Samarsky-Bykhovets, as the Chief of Staff of the Russian Corps of Mining Engineers, had granted access for two German mineralogists, the brothers Gustav and Heinrich Rose, to study the mineral samples from the Urals. Samarium was thus the first chemical element to be named after a person. The word samaria is sometimes used to mean samarium(III) oxide, by analogy with yttria, zirconia, alumina, ceria, holmia, etc. The symbol Sm was suggested for samarium, but an alternative Sa was often used instead until the 1920s.

Before the advent of ion-exchange separation technology in the 1950s, pure samarium had no commercial uses. However, a by-product of fractional crystallization purification of neodymium was a mix of samarium and gadolinium that got the name "Lindsay Mix" after the company that made it, and was used for nuclear control rods in some early nuclear reactors. Nowadays, a similar commodity product has the name "samarium-europium-gadolinium" (SEG) concentrate. It is prepared by solvent extraction from the mixed lanthanides isolated from bastnäsite (or monazite). Since heavier lanthanides have more affinity for the solvent used, they are easily extracted from the bulk using relatively small proportions of solvent. Not all rare-earth producers who process bastnäsite do so on a large enough scale to continue by separating the components of SEG, which typically makes up only 1Template:Endash2% of the original ore. Such producers therefore make SEG with a view to marketing it to the specialized processors. In this manner, the valuable europium in the ore is rescued for use in making phosphor. Samarium purification follows the removal of the europium. Template:As of, being in oversupply, samarium oxide is cheaper on a commercial scale than its relative abundance in the ore might suggest.

Occurrence and production

Samarskite

Samarskite

Samarium concentration in soils varies between 2 and 23 ppm, and oceans contain about 0.5–0.8 parts per trillion. The median value for its abundance in the Earth's crust used by the CRC Handbook is 7Template:Nbspparts per million (ppm) and is the 40th most abundant element. Distribution of samarium in soils strongly depends on its chemical state and is very inhomogeneous: in sandy soils, samarium concentration is about 200 times higher at the surface of soil particles than in the water trapped between them, and this ratio can exceed 1,000 in clays.

Samarium is not found free in nature, but, like other rare earth elements, is contained in many minerals, including monazite, bastnäsite, cerite, gadolinite and samarskite; monazite (in which samarium occurs at concentrations of up to 2.8%) and bastnäsite are mostly used as commercial sources. World resources of samarium are estimated at two million tonnes; they are mostly located in China, US, Brazil, India, Sri Lanka and Australia, and the annual production is about 700 tonnes. Country production reports are usually given for all rare-earth metals combined. By far, China has the largest production with 120,000 tonnes mined per year; it is followed by the US (about 5,000 tonnes) and India (2,700 tonnes). Samarium is usually sold as oxide, which at the price of about US$30/kg is one of the cheapest lanthanide oxides. Whereas mischmetal – a mixture of rare earth metals containing about 1% of samarium – has long been used, relatively pure samarium has been isolated only recently, through ion exchange processes, solvent extraction techniques, and electrochemical deposition. The metal is often prepared by electrolysis of a molten mixture of samarium(III) chloride with sodium chloride or calcium chloride. Samarium can also be obtained by reducing its oxide with lanthanum. The product is then distilled to separate samarium (boiling point 1,794 °C) and lanthanum (b.p. 3,464 °C).

Very few minerals have samarium being the most dominant element. Minerals with essential (dominant) samarium include monazite-(Sm) and florencite-(Sm). These minerals are very rare and are usually found containing other elements, usually cerium or neodymium. It is also made by neutron capture by samarium-149, which is added to the control rods of nuclear reactors. Therefore, ¹⁵¹Sm is present in spent nuclear fuel and radioactive waste.

Separating samarium from minerals involves nearly 100 individual processes and extremely strong acids.

Geopolitics

Western militaries across the world relied on a single samarium production plant in La Rochelle, France from the 1970s until the plant's closure in 1994. The facility sourced its samarium from Australia. A $1Template:Nbspbillion United States government effort to re-open a closed rare earths mine in Mountain Pass, California resulted in the facility going bankrupt.

Template:Asof, China produces all of the world's usable samarium; refining is concentrated in Baotou. The Biden administration signed two contracts for samarium production plants in the United States, but neither materialized. During US president Donald Trump's second-term tariff war, China leveled strict limits on the export of samarium, among other rare earth metals, as part of the long-running rare earths trade dispute (and larger trade war) between the two nations.

Applications

Magnets

An important use of samarium is samarium–cobalt magnets, which are nominally Template:Chem2 or Template:Chem2. They have high permanent magnetization, about 10,000 times that of iron and second only to neodymium magnets. However, samarium magnets resist demagnetization better; they are stable to temperatures above Template:Convert (cf. 300–400 °C for neodymium magnets). These magnets are found in small motors, headphones, and high-end magnetic pickups for guitars and related musical instruments. For example, they are used in the motors of a solar-powered electric aircraft, the Solar Challenger, and in the Samarium Cobalt Noiseless electric guitar and bass pickups.

Due to their heat resistance, samarium magnets are also used for military applications and are needed to manufacture modern aircraft and missiles. A single F-35 fighter jet contains about Template:Conv of samarium magnets.

Chemical reagent

Barbier reaction using samarium diiodide

Barbier reaction using Template:Chem2

Samarium and its compounds are important as catalysts and chemical reagents. Samarium catalysts help the decomposition of plastics, dechlorination of pollutants such as polychlorinated biphenyls (PCB), as well as dehydration and dehydrogenation of ethanol. Samarium(III) triflate Template:Chem2, that is Template:Chem2, is one of the most efficient Lewis acid catalysts for a halogen-promoted Friedel–Crafts reaction with alkenes. Samarium(II) iodide is a very common reducing and coupling agent in organic synthesis, for example in desulfonylation reactions; annulation; Danishefsky, Kuwajima, Mukaiyama and Holton Taxol total syntheses; strychnine total synthesis; Barbier reaction and other reductions with samarium(II) iodide.

In its usual oxidized form, samarium is added to ceramics and glasses where it increases absorption of infrared light. As a (minor) part of mischmetal, samarium is found in the "flint" ignition devices of many lighters and torches.

Neutron absorber

Samarium-149 has a high cross section for neutron capture (41,000 barns) and so is used in control rods of nuclear reactors. Its advantage compared to competing materials, such as boron and cadmium, is stability of absorption – most of the fusion products of ¹⁴⁹Sm are other isotopes of samarium that are also good neutron absorbers. For example, the cross section of samarium-151 is 15,000 barns, it is on the order of hundreds of barns for ¹⁵⁰Sm, ¹⁵²Sm, and ¹⁵³Sm, and 6,800 barns for natural (mixed-isotope) samarium.

Lasers

Samarium-doped calcium fluoride crystals were used as an active medium in one of the first solid-state lasers designed and built by Peter Sorokin (co-inventor of the dye laser) and Mirek Stevenson at IBM research labs in early 1961. This samarium laser gave pulses of red light at 708.5 nm. It had to be cooled by liquid helium and so did not find practical applications. Another samarium-based laser became the first saturated X-ray laser operating at wavelengths shorter than 10 nanometers. It gave 50-picosecond pulses at 7.3 and 6.8 nm suitable for uses in holography, high-resolution microscopy of biological specimens, deflectometry, interferometry, and radiography of dense plasmas related to confinement fusion and astrophysics. Saturated operation meant that the maximum possible power was extracted from the lasing medium, resulting in the high peak energy of 0.3 mJ. The active medium was samarium plasma produced by irradiating samarium-coated glass with a pulsed infrared Nd-glass laser (wavelength ~1.05 μm).

Storage phosphor

In 2007 it was shown that nanocrystalline BaFCl:Sm³⁺ as prepared by co-precipitation can serve as a very efficient X-ray storage phosphor. The co-precipitation leads to nanocrystallites of the order of 100–200 nm in size and their sensitivity as X-ray storage phosphors is increased a remarkable ~500,000 times because of the specific arrangements and density of defect centers in comparison with microcrystalline samples prepared by sintering at high temperature. The mechanism is based on reduction of Sm³⁺ to Sm²⁺ by trapping electrons that are created upon exposure to ionizing radiation in the BaFCl host. The ⁵D_J–⁷F_J f–f luminescence lines can be very efficiently excited via the parity allowed 4f⁶→4f⁵5d transition at ~417 nm. The latter wavelength is ideal for efficient excitation by blue-violet laser diodes as the transition is electric dipole allowed and thus relatively intense (400 L/(mol⋅cm)). The phosphor has potential applications in personal dosimetry, dosimetry and imaging in radiotherapy, and medical imaging.

Non-commercial and potential uses

• The change in electrical resistivity in samarium monochalcogenides can be used in a pressure sensor or in a memory device triggered between a low-resistance and high-resistance state by external pressure, and such devices are being developed commercially. Samarium monosulfide also generates electric voltage upon moderate heating to about Template:Convert that can be applied in thermoelectric power converters.
• Analysis of relative concentrations of samarium and neodymium isotopes ¹⁴⁷Sm, ¹⁴⁴Nd, and ¹⁴³Nd allows determination of the age and origin of rocks and meteorites in samarium–neodymium dating. Both elements are lanthanides and are very similar physically and chemically. Thus, Sm–Nd dating is either insensitive to partitioning of the marker elements during various geologic processes, or such partitioning can well be understood and modeled from the ionic radii of said elements.
• The Sm³⁺ ion is a potential activator for use in warm-white light emitting diodes. It offers high luminous efficacy due to narrow emission bands; but the generally low quantum efficiency and too little absorption in the UV-A to blue spectral region hinders commercial application.
• Samarium is used for ionosphere testing. A rocket spreads samarium monoxide as a red vapor at high altitude, and researchers test how the atmosphere disperses it and how it impacts radio transmissions.
• Samarium hexaboride, Template:Chem2, has recently been shown to be a topological insulator with potential uses in quantum computing.

Biological role and precautions

Template:Chembox Samarium salts stimulate metabolism, but it is unclear whether this is from samarium or other lanthanides present with it. The total amount of samarium in adults is about 50 μg, mostly in liver and kidneys and with ~8 μg/L being dissolved in blood. Samarium is not absorbed by plants to a measurable concentration and so is normally not part of human diet. However, a few plants and vegetables may contain up to 1 part per million of samarium. Insoluble salts of samarium are non-toxic and the soluble ones are only slightly toxic. When ingested, only 0.05% of samarium salts are absorbed into the bloodstream and the remainder are excreted. From the blood, 45% goes to the liver and 45% is deposited on the surface of the bones where it remains for 10 years; the remaining 10% is excreted.

External links

• It's Elemental – Samarium
• Reducing Agents > Samarium low valent