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Samarium: the story on HearLore | HearLore
Samarium
The first chemical element to be named after a living person was not named for a scientist or a king, but for a Russian mining official who never knew his name would outlive him. In 1879, French chemist Paul-Émile Lecoq de Boisbaudran isolated a new element from the mineral samarskite, which he had obtained from the Ural Mountains. He chose to name this element samarium after Colonel Vassili Samarsky-Bykhovets, the Chief of Staff of the Russian Corps of Mining Engineers. Samarsky-Bykhovets had granted access to two German mineralogists, the brothers Gustav and Heinrich Rose, to study samples from the Ural Mountains in the 1840s. This indirect honor made Samarsky-Bykhovets the first person to have a chemical element named after him, a distinction that would remain unique for decades. The discovery itself was a race against time and other chemists. While Swiss chemist Marc Delafontaine had announced a new element called decipium in 1878, he later admitted in 1880 that his discovery was actually a mixture of several elements, one of which was identical to Boisbaudran's samarium. The pure samarium(III) oxide was not produced until 1901 by Eugène-Anatole Demarçay, and the element itself was isolated in its metallic form by Wilhelm Muthmann in 1903. The symbol Sm was eventually adopted, replacing the alternative Sa that was used until the 1920s, cementing the element's identity in the periodic table.
A Metal Of Many Faces
Samarium is a moderately hard, silvery metal that behaves in ways that seem contradictory to its classification as a rare earth element. When freshly prepared, it possesses a bright silvery lustre, but it slowly oxidizes in air to form a dull grayish-yellow powder of oxide-hydroxide mixture. This oxidation happens even when the metal is stored under mineral oil, requiring it to be sealed under an inert gas like argon to preserve its metallic appearance. Its physical properties are equally complex, with a boiling point of 1,794 degrees Celsius making it the third most volatile lanthanide after ytterbium and europium. This volatility is actually a key factor in separating samarium from its ores. The metal exhibits a remarkable ability to change its crystal structure under different conditions. At room temperature, it has a rhombohedral structure, but upon heating to 733 degrees Celsius, it transforms into a hexagonal close-packed phase. Further heating to 922 degrees Celsius turns it into a body-centered cubic phase. Under extreme pressure, such as 40 kilobars, it adopts a double-hexagonally close-packed structure, and pressures of hundreds of kilobars can induce a tetragonal phase. These phase transformations are not just academic curiosities; they demonstrate the unique electronic behavior of samarium, which has one of the largest atomic radii of all elements at 238 picometers. Only potassium, praseodymium, barium, rubidium, and caesium are larger. This large size and its specific electron configuration allow samarium to exist in multiple oxidation states, most commonly +3, but also +2, which is rare among lanthanides and gives it unique chemical reactivity.
Who was the Russian mining official that samarium was named after?
Samarium was named after Colonel Vassili Samarsky-Bykhovets, the Chief of Staff of the Russian Corps of Mining Engineers. He granted access to German mineralogists Gustav and Heinrich Rose to study samples from the Ural Mountains in the 1840s. This indirect honor made him the first person to have a chemical element named after him.
When was samarium first isolated and what was its symbol history?
French chemist Paul-Émile Lecoq de Boisbaudran isolated samarium from samarskite in 1879. The pure samarium(III) oxide was produced in 1901 by Eugène-Anatole Demarçay, and the metallic form was isolated by Wilhelm Muthmann in 1903. The symbol Sm was adopted in the 1920s, replacing the alternative Sa.
What are the physical properties and crystal structures of samarium?
Samarium is a moderately hard, silvery metal with a boiling point of 1,794 degrees Celsius and an atomic radius of 238 picometers. It exhibits multiple crystal structures including rhombohedral at room temperature, hexagonal close-packed at 733 degrees Celsius, and body-centered cubic at 922 degrees Celsius. Under extreme pressure of 40 kilobars, it adopts a double-hexagonally close-packed structure.
How is samarium used in nuclear reactors and what is samarium-149?
Samarium-149 is a potent neutron absorber with a cross section of 41,000 barns for thermal neutrons that builds up to an equilibrium concentration over about 500 hours. It is used in control rods for nuclear reactors and is a decay product of neodymium-149. The isotope is not radioactive and does not vanish through decay, creating a neutron poison effect that must be managed.
How is samarium-153 used in cancer treatment and what is the drug name?
Samarium-153 is a beta emitter with a half-life of 46.285 hours used to treat metastatic bone cancer in lung, prostate, breast, and osteosarcoma cases. It is chelated with ethylene diamine tetramethylene phosphonate to form the drug samarium-153 lexidronam, known by the trade name Quadramet. The drug is injected intravenously and targets cancer cells in bones where 45% of the samarium is deposited.
What is the samarium-neodymium dating method and how does it work?
The samarium-neodymium dating method relies on the analysis of relative concentrations of samarium-147 and neodymium-143 isotopes. Samarium-147 is an extremely long-lived radioisotope with a half-life of 1.066 billion years that undergoes alpha decay to neodymium-143. This process determines the age and origin of rocks and meteorites and is useful because both elements are lanthanides with similar physical and chemical properties.
The most commercially significant application of samarium is found in the samarium-cobalt magnet, a material that holds a permanent magnetization second only to neodymium magnets but with a critical advantage: heat resistance. While neodymium magnets lose their magnetic properties at temperatures between 300 and 400 degrees Celsius, samarium-cobalt magnets remain stable at temperatures above 750 degrees Celsius. This property makes them indispensable for high-temperature environments where other magnets would fail. They are used in the motors of solar-powered electric aircraft like the Solar Challenger, in high-end magnetic pickups for guitars and basses, and in the complex systems of modern military hardware. A single F-35 fighter jet contains approximately 1.5 kilograms of samarium magnets, essential for the guidance systems and motors of missiles and aircraft. The geopolitical stakes of this material are high. Western militaries relied on a single production plant in La Rochelle, France, for samarium from the 1970s until its closure in 1994. The facility sourced its samarium from Australia, but the supply chain was fragile. A billion-dollar United States government effort to reopen a rare earths mine in Mountain Pass, California, resulted in the facility going bankrupt. Today, China produces all of the world's usable samarium, with refining concentrated in Baotou. During the trade disputes of the Trump administration, China imposed strict limits on the export of samarium, leveraging its dominance to exert pressure in the ongoing rare earths trade war. The element's scarcity in pure form, requiring nearly 100 individual processes and extremely strong acids to separate from minerals, further complicates its availability. Despite being the 40th most abundant element in the Earth's crust, with world resources estimated at two million tonnes, the annual production is only about 700 tonnes, with China accounting for 120,000 tonnes mined per year, dwarfing the output of the United States and India.
The Nuclear Absorber
Beneath the surface of nuclear reactor operations lies a quiet but critical role played by the isotope samarium-149. This isotope is a potent neutron absorber with a cross section of 41,000 barns for thermal neutrons, making it second in importance only to xenon-135 for reactor design and operation. Unlike xenon-135, which decays rapidly, samarium-149 is not radioactive and does not vanish through decay. Instead, it builds up to an equilibrium concentration during reactor operations over a period of about 500 hours, or three weeks. This accumulation creates a neutron poison effect that must be carefully managed to maintain reactor stability. The advantage of samarium-149 over competing materials like boron and cadmium is the stability of its absorption. Most fusion products of samarium-149 are other isotopes of samarium that are also effective neutron absorbers. For instance, the cross section of samarium-151 is 15,000 barns, and natural samarium has a cross section of 6,800 barns. This property makes it an ideal component for control rods in nuclear reactors. The isotope is also a decay product of the fission product neodymium-149, and its presence in spent nuclear fuel and radioactive waste presents unique challenges for long-term storage and disposal. The study of samarium-149 is crucial for understanding the behavior of nuclear reactors and ensuring their safe operation. The element's role in nuclear technology extends beyond control rods; it is also used in the development of X-ray lasers and in the study of high-temperature superconductors. The interaction of samarium with neutrons is a key factor in the design and operation of modern nuclear reactors, highlighting the element's importance in the energy sector.
The Cancer Killer
In the field of medicine, samarium-153 has emerged as a powerful tool in the fight against cancer. This isotope is a beta emitter with a half-life of 46.285 hours, and it is used to kill cancer cells in lung cancer, prostate cancer, breast cancer, and osteosarcoma. The isotope is chelated with ethylene diamine tetramethylene phosphonate, forming a drug known as samarium-153 lexidronam, with the trade name Quadramet. The chelation process is critical, as it prevents the radioactive samarium from accumulating in the body, which would result in excessive irradiation and the generation of new cancer cells. The drug is injected intravenously and targets cancer cells that have spread to the bones, where 45% of the samarium is deposited. The remaining 10% is excreted, while 45% goes to the liver. The total amount of samarium in adults is about 50 micrograms, mostly found in the liver and kidneys, with approximately 8 micrograms per liter dissolved in the blood. The use of samarium-153 in cancer treatment represents a significant advancement in targeted radiotherapy, offering a way to treat metastatic bone cancer with minimal damage to surrounding healthy tissue. The element's ability to be chelated and its specific decay properties make it an ideal candidate for this application. The development of samarium-153 as a therapeutic agent has saved countless lives and continues to be a subject of research and improvement in the field of oncology.
The Quantum Mystery
Beyond its practical applications, samarium holds a place in the frontiers of quantum physics and materials science. Samarium hexaboride, or SmB6, is a typical intermediate-valence compound where samarium exists as both Sm2+ and Sm3+ ions in a 3:7 ratio. This material belongs to a class of Kondo insulators, which exhibit metallic electrical conductivity at temperatures above 50 Kelvin but behave as non-magnetic insulators at lower temperatures. The cooling-induced metal-insulator transition in SmB6 is accompanied by a sharp increase in thermal conductivity, peaking at about 15 Kelvin. This phenomenon is due to the fact that electrons do not contribute to thermal conductivity at low temperatures, which is instead dominated by phonons. The decrease in electron concentration reduces the rate of electron-phonon scattering, leading to the observed increase in thermal conductivity. Recent research has shown that samarium hexaboride is a topological insulator with potential uses in quantum computing. The element's unique electronic properties also make it a candidate for use in pressure sensors and memory devices, where changes in electrical resistivity can be triggered by external pressure. Samarium-doped calcium fluoride crystals were used in one of the first solid-state lasers designed by Peter Sorokin and Mirek Stevenson at IBM research labs in early 1961, giving pulses of red light at 708.5 nanometers. Another samarium-based laser became the first saturated X-ray laser operating at wavelengths shorter than 10 nanometers, suitable for uses in holography, high-resolution microscopy, and radiography of dense plasmas. The element's role in these advanced technologies highlights its importance in the development of future scientific instruments and quantum devices.
The Geological Clock
Samarium plays a crucial role in the dating of rocks and meteorites through the samarium-neodymium dating method. This technique relies on the analysis of relative concentrations of samarium and neodymium isotopes, specifically samarium-147 and neodymium-143. Samarium-147 is an extremely long-lived radioisotope with a half-life of 1.066 billion years, and it undergoes alpha decay to neodymium-143. This decay process is used to determine the age and origin of rocks and meteorites. The method is particularly useful because both samarium and neodymium are lanthanides and are very similar physically and chemically. This similarity means that samarium-neodymium dating is either insensitive to the partitioning of the marker elements during various geologic processes, or such partitioning can be well understood and modeled from the ionic radii of the elements. The technique has been instrumental in understanding the formation of the Earth and the solar system, providing insights into the age of the oldest rocks and the timing of geological events. The presence of samarium-146, an extinct radionuclide with a half-life of 9.20 years, has also been the subject of searches for primordial nuclides. Although it is no longer present in nature, the study of samarium-146 has provided valuable information about the early history of the solar system. The element's role in geochronology underscores its importance in the field of earth sciences and our understanding of the planet's history.