Holmium

Holmium is a chemical element with symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare-earth element. Holmium was discovered by Swedish chemist Per Theodor Cleve. Its oxide was first isolated from rare-earth ores in 1878. The element's name comes from Holmia, the Latin name for the city of Stockholm.

Elemental holmium is a relatively soft and malleable silvery-white metal. It is too reactive to be found uncombined in nature, but when isolated, is relatively stable in dry air at room temperature. However, it reacts with water and corrodes readily and also burns in air when heated.

Holmium is found in the minerals monazite and gadolinite and is usually commercially extracted from monazite using ion-exchange techniques. Its compounds in nature and in nearly all of its laboratory chemistry are trivalently oxidized, containing Ho(III) ions. Trivalent holmium ions have fluorescent properties similar to many other rare-earth ions (while yielding their own set of unique emission light lines), and thus are used in the same way as some other rare earths in certain laser and glass-colorant applications.

Holmium has the highest magnetic permeability of any element and therefore is used for the polepieces of the strongest static magnets. Because holmium strongly absorbs neutrons, it is also used as a burnable poison in nuclear reactors.

Holmium,  67Ho
Holmium2
Holmium
Pronunciation/ˈhoʊlmiəm/ (HOHL-mee-əm)
Appearancesilvery white
Standard atomic weight Ar, std(Ho)164.930328(7)[1]
Holmium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Ho

Es
dysprosiumholmiumerbium
Atomic number (Z)67
Groupgroup n/a
Periodperiod 6
Blockf-block
Element category  lanthanide
Electron configuration[Xe] 4f11 6s2
Electrons per shell
2, 8, 18, 29, 8, 2
Physical properties
Phase at STPsolid
Melting point1734 K ​(1461 °C, ​2662 °F)
Boiling point2873 K ​(2600 °C, ​4712 °F)
Density (near r.t.)8.79 g/cm3
when liquid (at m.p.)8.34 g/cm3
Heat of fusion17.0 kJ/mol
Heat of vaporization251 kJ/mol
Molar heat capacity27.15 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1432 1584 (1775) (2040) (2410) (2964)
Atomic properties
Oxidation states+1, +2, +3 (a basic oxide)
ElectronegativityPauling scale: 1.23
Ionization energies
  • 1st: 581.0 kJ/mol
  • 2nd: 1140 kJ/mol
  • 3rd: 2204 kJ/mol
Atomic radiusempirical: 176 pm
Covalent radius192±7 pm
Color lines in a spectral range
Spectral lines of holmium
Other properties
Natural occurrenceprimordial
Crystal structurehexagonal close-packed (hcp)
Hexagonal close packed crystal structure for holmium
Speed of sound thin rod2760 m/s (at 20 °C)
Thermal expansionpoly: 11.2 µm/(m·K) (at r.t.)
Thermal conductivity16.2 W/(m·K)
Electrical resistivitypoly: 814 nΩ·m (at r.t.)
Magnetic orderingparamagnetic
Young's modulus64.8 GPa
Shear modulus26.3 GPa
Bulk modulus40.2 GPa
Poisson ratio0.231
Vickers hardness410–600 MPa
Brinell hardness500–1250 MPa
CAS Number7440-60-0
History
DiscoveryJacques-Louis Soret (1878)
Main isotopes of holmium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
163Ho syn 4570 y ε 163Dy
164Ho syn 29 min ε 164Dy
165Ho 100% stable
166Ho syn 26.763 h β 166Er
167Ho syn 3.1 h β 167Er

Characteristics

Physical properties

Holmium(III) oxide
Ho2O3, left: natural light, right: under a cold-cathode fluorescent lamp

Holmium is a relatively soft and malleable element that is fairly corrosion-resistant and stable in dry air at standard temperature and pressure. In moist air and at higher temperatures, however, it quickly oxidizes, forming a yellowish oxide. In pure form, holmium possesses a metallic, bright silvery luster.

Holmium oxide has some fairly dramatic color changes depending on the lighting conditions. In daylight, it has a tannish yellow color. Under trichromatic light, it is fiery orange-red, almost indistinguishable from the appearance of erbium oxide under the same lighting conditions. The perceived color change is related to the sharp absorption bands of holmium interacting with a subset of the sharp emission bands of the trivalent ions of europium and terbium, acting as phosphors.[2]

Holmium has the highest magnetic moment (10.6 µ
B
) of any naturally occurring element and possesses other unusual magnetic properties. When combined with yttrium, it forms highly magnetic compounds.[3] Holmium is paramagnetic at ambient conditions, but is ferromagnetic at temperatures below 19 K.[4]

Chemical properties

Holmium metal tarnishes slowly in air and burns readily to form holmium(III) oxide:

4 Ho + 3 O2 → 2 Ho2O3

Holmium is quite electropositive and is generally trivalent. It reacts slowly with cold water and quite quickly with hot water to form holmium hydroxide:

2 Ho (s) + 6 H2O (l) → 2 Ho(OH)3 (aq) + 3 H2 (g)

Holmium metal reacts with all the halogens:

2 Ho (s) + 3 F2 (g) → 2 HoF3 (s) [pink]
2 Ho (s) + 3 Cl2 (g) → 2 HoCl3 (s) [yellow]
2 Ho (s) + 3 Br2 (g) → 2 HoBr3 (s) [yellow]
2 Ho (s) + 3 I2 (g) → 2 HoI3 (s) [yellow]

Holmium dissolves readily in dilute sulfuric acid to form solutions containing the yellow Ho(III) ions, which exist as a [Ho(OH2)9]3+ complexes:[5]

2 Ho (s) + 3 H2SO4 (aq) → 2 Ho3+ (aq) + 3 SO2−
4
(aq) + 3 H2 (g)

Holmium's most common oxidation state is +3. Holmium in solution is in the form of Ho3+ surrounded by nine molecules of water. Holmium dissolves in acids.[6]

Isotopes

Natural holmium contains one stable isotope, holmium-165. Some synthetic radioactive isotopes are known; the most stable one is holmium-163, with a half-life of 4570 years. All other radioisotopes have ground-state half-lives not greater than 1.117 days, and most have half-lives under 3 hours. However, the metastable 166m1Ho has a half-life of around 1200 years because of its high spin. This fact, combined with a high excitation energy resulting in a particularly rich spectrum of decay gamma rays produced when the metastable state de-excites, makes this isotope useful in nuclear physics experiments as a means for calibrating energy responses and intrinsic efficiencies of gamma ray spectrometers.

History

Holmium (Holmia, Latin name for Stockholm) was discovered by Jacques-Louis Soret and Marc Delafontaine in 1878 who noticed the aberrant spectrographic absorption bands of the then-unknown element (they called it "Element X").[7][8] The following year, Per Teodor Cleve independently discovered the element while he was working on erbia earth (erbium oxide).[9][10]

Using the method developed by Carl Gustaf Mosander, Cleve first removed all of the known contaminants from erbia. The result of that effort was two new materials, one brown and one green. He named the brown substance holmia (after the Latin name for Cleve's home town, Stockholm) and the green one thulia. Holmia was later found to be the holmium oxide, and thulia was thulium oxide.[11] In Henry Moseley's classic paper on atomic numbers, holmium was assigned an atomic number of 66. Evidently, the holmium preparation he had been given to investigate had been grossly impure, dominated by neighboring (and unplotted) dysprosium. He would have seen x-ray emission lines for both elements, but assumed that the dominant ones belonged to holmium, instead of the dysprosium impurity.

Occurrence and production

Like all other rare earths, holmium is not naturally found as a free element. It does occur combined with other elements in gadolinite (the black part of the specimen illustrated to the right), monazite and other rare-earth minerals. No holmium-dominant mineral has yet been found.[12] The main mining areas are China, United States, Brazil, India, Sri Lanka, and Australia with reserves of holmium estimated as 400,000 tonnes.[11]

Holmium makes up 1.4 parts per million of the Earth's crust by mass. This makes it the 56th most abundant element in the Earth's crust. Holmium makes up 1 part per million of the soils, 400 parts per quadrillion of seawater, and almost none of Earth's atmosphere. Holmium is rare for a lanthanide.[13] It makes up 500 parts per trillion of the universe by mass.[14]

It is commercially extracted by ion exchange from monazite sand (0.05% holmium), but is still difficult to separate from other rare earths. The element has been isolated through the reduction of its anhydrous chloride or fluoride with metallic calcium.[15] Its estimated abundance in the Earth's crust is 1.3 mg/kg. Holmium obeys the Oddo–Harkins rule: as an odd-numbered element, it is less abundant than its immediate even-numbered neighbors, dysprosium and erbium. However, it is the most abundant of the odd-numbered heavy lanthanides. The principal current source are some of the ion-adsorption clays of southern China. Some of these have a rare-earth composition similar to that found in xenotime or gadolinite. Yttrium makes up about 2/3 of the total by mass; holmium is around 1.5%. The original ores themselves are very lean, maybe only 0.1% total lanthanide, but are easily extracted.[16] Holmium is relatively inexpensive for a rare-earth metal with the price about 1000 USD/kg.[17]

Applications

HoOxideSolution
A solution of 4% holmium oxide in 10% perchloric acid, permanently fused into a quartz cuvette as an optical calibration standard

Holmium has the highest magnetic strength of any element, and therefore is used to create the strongest artificially generated magnetic fields, when placed within high-strength magnets as a magnetic pole piece (also called a magnetic flux concentrator).[18] Since it can absorb nuclear fission-bred neutrons, it is also used as a burnable poison to regulate nuclear reactors.[11]

Holmium-doped yttrium iron garnet (YIG) and yttrium lithium fluoride (YLF) have applications in solid-state lasers, and Ho-YIG has applications in optical isolators and in microwave equipment (e.g., YIG spheres). Holmium lasers emit at 2.1 micrometres.[19] They are used in medical, dental, and fiber-optical applications.[3]

Holmium is one of the colorants used for cubic zirconia and glass, providing yellow or red coloring.[20] Glass containing holmium oxide and holmium oxide solutions (usually in perchloric acid) have sharp optical absorption peaks in the spectral range 200–900 nm. They are therefore used as a calibration standard for optical spectrophotometers[21] and are available commercially.[22]

The radioactive but long-lived 166m1Ho (see "Isotopes" above) is used in calibration of gamma-ray spectrometers.[23]

In March 2017, IBM announced that they have developed a technique to store one bit of data on a single Holmium atom set on a bed of magnesium oxide.[24]

Biological role

Holmium plays no biological role in humans, but its salts are able to stimulate metabolism.[15] Humans typically consume about a milligram of holmium a year. Plants do not readily take up holmium from the soil. Some vegetables have had their holmium content measured, and it amounted to 100 parts per trillion.[6]

Toxicity

Large amounts of holmium salts can cause severe damage if inhaled, consumed orally, or injected. The biological effects of holmium over a long period of time are not known. Holmium has a low level of acute toxicity.[25]

See also

  • Holmium compounds

References

  1. ^ Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
  2. ^ Yiguo Su; Li, Guangshe; Chen, Xiaobo; Liu, Junjie; Li, Liping (2008). "Hydrothermal Synthesis of GdVO4:Ho3+ Nanorods with a Novel White-light Emission". Chemistry Letters. 37 (7): 762–763. doi:10.1246/cl.2008.762.
  3. ^ a b C. K. Gupta; Nagaiyar Krishnamurthy (2004). Extractive metallurgy of rare earths. CRC Press. p. 32. ISBN 0-415-33340-7.
  4. ^ Jiles, David (1998). Introduction to magnetism and magnetic materials. CRC Press. p. 228. ISBN 0-412-79860-3.
  5. ^ "Chemical reactions of Holmium". Webelements. Retrieved 2009-06-06.
  6. ^ a b Emsley, John (2011). Nature's Building Blocks.
  7. ^ Jacques-Louis Soret (1878). "Sur les spectres d'absorption ultra-violets des terres de la gadolinite". Comptes rendus de l'Académie des sciences. 87: 1062.
  8. ^ Jacques-Louis Soret (1879). "Sur le spectre des terres faisant partie du groupe de l'yttria". Comptes rendus de l'Académie des sciences. 89: 521.
  9. ^ Per Teodor Cleve (1879). "Sur deux nouveaux éléments dans l'erbine". Comptes rendus de l'Académie des sciences. 89: 478–480. Cleve named holmium on p. p. 480: "Je propose pour ce métal le nom de holmium, Ho, dérivé du nom latinisé de Stockholm, dont les environs renferment tant de minéraux riches en yttria." (I propose for this metal the name of "holmium", Ho, [which is] derived from the Latin name for Stockholm, the environs of which contain so many minerals rich in yttrium.)
  10. ^ Per Teodor Cleve (1879). "Sur l'erbine". Comptes rendus de l'Académie des sciences. 89: 708.
  11. ^ a b c John Emsley (2001). Nature's building blocks: an A-Z guide to the elements. US: Oxford University Press. pp. 181–182. ISBN 0-19-850341-5.
  12. ^ Hudson Institute of Mineralogy (1993–2018). "Mindat.org". www.mindat.org. Retrieved 14 January 2018.
  13. ^ Emsley, John (2011). Nature's Building Blocks. Oxford University Press.
  14. ^ Ltd, Mark Winter, University of Sheffield and WebElements. "WebElements Periodic Table » Periodicity » Abundance in the universe » periodicity". www.webelements.com. Archived from the original on 2017-09-29. Retrieved 27 March 2018.
  15. ^ a b C. R. Hammond (2000). The Elements, in Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 0-8493-0481-4.
  16. ^ Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. pp. 338–339. ISBN 0-07-049439-8. Retrieved 2009-06-06.
  17. ^ James B. Hedrick. "Rare-Earth Metals" (PDF). USGS. Retrieved 2009-06-06.
  18. ^ R. W. Hoard; S. C. Mance; R. L. Leber; E. N. Dalder; M. R. Chaplin; K. Blair; et al. (1985). "FIELD ENHANCEMENT OF A 12.5-T MAGNET USING HOLMIUM POLES". IEEE Transactions on Magnetics. 21 (2): 448–450. Bibcode:1985ITM....21..448H. doi:10.1109/tmag.1985.1063692.
  19. ^ Wollin, T. A.; Denstedt, J. D. (Feb 1998). "The holmium laser in urology". Journal of clinical laser medicine & surgery. 16 (1): 13–20. doi:10.1089/clm.1998.16.13. PMID 9728125.
  20. ^ "Cubic zirconia". Archived from the original on 2009-04-24. Retrieved 2009-06-06.
  21. ^ R. P. MacDonald (1964). "Uses for a Holmium Oxide Filter in Spectrophotometry" (PDF). Clinical Chemistry. 10 (12): 1117–20. PMID 14240747.
  22. ^ "Holmium Glass Filter for Spectrophotometer Calibration". Archived from the original on 2010-03-14. Retrieved 2009-06-06.
  23. ^ Ming-Chen Yuan; Jeng-Hung Lee & Wen-Song Hwang (2002). "The absolute counting of 166mHo, 58Co and 88Y". Applied Radiation and Isotopes. 56: 424. doi:10.1016/S0969-8043(01)00226-3.
  24. ^ "Storing data in a single atom proved possible by IBM researchers". Retrieved 2017-03-10.
  25. ^ "Holmium" in Periodic Table v2.5. University of Coimbra, Portugal
  • Guide to the Elements – Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1

External links

Branching fraction

In particle physics and nuclear physics, the branching fraction (or branching ratio) for a decay is the fraction of particles which decay by an individual decay mode with respect to the total number of particles which decay. It is equal to the ratio of the partial decay constant to the overall decay constant. Sometimes a partial half-life is given, but this term is misleading; due to competing modes it is not true that half of the particles will decay through a particular decay mode after its partial half-life. The partial half-life is merely an alternate way to specify the partial decay constant λ, the two being related through:

For example, for spontaneous decays of 132Cs, 98.1% are ε or β+ decays, and 1.9% are β− decays. The partial decay constants can be calculated from the branching fraction and the half-life of 132Cs (6.479 d), they are: 0.10 d−1 (ε + β+) and .0020 d−1). The partial half-lives are 6.60 d (ε + β+) and 341 d (β). Here the problem with the term partial half-life is evident: after (341+6.60) days almost all the nuclei will have decayed, not only half as one may initially think.

Isotopes with significant branching of decay modes include copper-64, arsenic-74, rhodium-102, indium-112, iodine-126 and holmium-164.

Dysprosium

Dysprosium is a chemical element with symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime. Naturally occurring dysprosium is composed of seven isotopes, the most abundant of which is 164Dy.

Dysprosium was first identified in 1886 by Paul Émile Lecoq de Boisbaudran, but it was not isolated in pure form until the development of ion exchange techniques in the 1950s. Dysprosium has relatively few applications where it cannot be replaced by other chemical elements. It is used for its high thermal neutron absorption cross-section in making control rods in nuclear reactors, for its high magnetic susceptibility in data storage applications, and as a component of Terfenol-D (a magnetostrictive material). Soluble dysprosium salts are mildly toxic, while the insoluble salts are considered non-toxic.

Dysprosium titanate

Dysprosium titanate (Dy2Ti2O7) is an inorganic compound, a ceramic of the titanate family, with pyrochlore structure. Its CAS number is 68993-46-4.

Dysprosium titanate, like holmium titanate and holmium stannate, is a spin ice material. In 2009, quasiparticles resembling magnetic monopoles were observed at low temperature and high magnetic field.Dysprosium titanate (Dy2TiO5) is used since 1995 as material for control rods of commercial nuclear reactor.

Erbium

Erbium is a chemical element with symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare earth element, originally found in the gadolinite mine in Ytterby in Sweden, from which it got its name.

Erbium's principal uses involve its pink-colored Er3+ ions, which have optical fluorescent properties particularly useful in certain laser applications. Erbium-doped glasses or crystals can be used as optical amplification media, where Er3+ ions are optically pumped at around 980 or 1480 nm and then radiate light at 1530 nm in stimulated emission. This process results in an unusually mechanically simple laser optical amplifier for signals transmitted by fiber optics. The 1550 nm wavelength is especially important for optical communications because standard single mode optical fibers have minimal loss at this particular wavelength.

In addition to optical fiber amplifier-lasers, a large variety of medical applications (i.e. dermatology, dentistry) rely on the erbium ion's 2940 nm emission (see Er:YAG laser) when lit at another wavelength, which is highly absorbed in water in tissues, making its effect very superficial. Such shallow tissue deposition of laser energy is helpful in laser surgery, and for the efficient production of steam which produces enamel ablation by common types of dental laser.

Holmium(III) bromide

Holmium(III) bromide is a crystalline compound made of one holmium atom and three bromine atoms. Holmium bromide is a yellow powder at room temperature. Holmium bromide is hygroscopic. Holmium bromide is odorless.

Holmium(III) chloride

Holmium(III) chloride is the inorganic compound with the formula HoCl3. It is a common salt but is mainly used in research. It exhibits the same color-changing behavior seen in holmium oxide, being a yellow in natural lighting and a bright pink color in fluorescent lighting.

Holmium(III) oxide

Holmium(III) oxide, or holmium oxide is a chemical compound of a rare-earth element holmium and oxygen with the formula Ho2O3. Together with dysprosium(III) oxide (Dy2O3) holmium oxide is one of the most powerfully paramagnetic substances known. The oxide, also called holmia, occurs as a component of the related erbium oxide mineral called erbia. Typically the oxides of the trivalent lanthanides coexist in nature and separation of these components requires specialized methods. Holmium oxide is used in making specialty colored glasses. Glass containing holmium oxide and holmium oxide solutions have a series of sharp optical absorption peaks in the visible spectral range. They are therefore traditionally used as a convenient calibration standard for optical spectrophotometers.

Holmium titanate

Holmium titanate is an inorganic compound with the chemical formula Ho2Ti2O7.

Holmium titanate is a spin ice material like dysprosium titanate and holmium stannate.

Holmium–magnesium–zinc quasicrystal

A holmium–magnesium–zinc (Ho–Mg–Zn) quasicrystal is a quasicrystal made of an alloy of the three metals holmium, magnesium and zinc that has the shape of a regular dodecahedron, a Platonic solid with 12 five-sided faces. Unlike the similar pyritohedron shape of some cubic-system crystals such as pyrite, this quasicrystal has faces that are true regular pentagons.

Isotopes of holmium

Natural holmium (67Ho) contains one stable isotope, 165Ho. A number of synthetic radioactive isotopes are known, the most stable one is 163Ho, with a half-life of 4,570 years. All other radioisotopes have half-lives not greater than 1.117 days in their ground states (although the metastable 166mHo has a half-life of about 1,200 years), and most have half-lives under 3 hours.

Laser lithotripsy

Laser lithotripsy is a surgical procedure to remove stones from urinary tract, i.e., kidney, ureter, bladder, or urethra.

Laser thermal keratoplasty

Laser thermal keratoplasty is a non-contact laser refractive surgery.

Major actinide

Major actinides is a term used in the nuclear power industry that refers to the plutonium and uranium present in used nuclear fuel, as opposed to the minor actinides neptunium, americium, curium, berkelium, and californium.

Marc Delafontaine

Marc Delafontaine (Born at Celigny, 1837–1911) was a Swiss chemist who in 1878, along with Jacques-Louis Soret, first observed holmium spectroscopically. In 1879, Per Teodor Cleve chemically separated it from thulium and erbium. The three are given credit for the element's discovery.

Per Teodor Cleve

Per Teodor Cleve (10 February 1840 – 18 June 1905) was a Swedish chemist, biologist, mineralogist and oceanographer. He is best known for his discovery of the chemical elements holmium and thulium.Born in Stockholm in 1840, Cleve earned his BSc and PhD from Uppsala University in 1863 and 1868, respectively. After receiving his PhD, he became an assistant professor of chemistry at the university. He later became professor of general and agricultural chemistry. In 1874 he theorised that didymium was in fact two elements; this theory was confirmed in 1885 when Carl Auer von Welsbach discovered neodymium and praseodymium.

In 1879 Cleve discovered holmium and thulium. His other contributions to chemistry include the discovery of aminonaphthalenesulfonic acids, also known as Cleve's acids. From 1890 on he focused on biological studies. He developed a method of determining the age and order of late glacial and postglacial deposits from the types of diatom fossils in the deposits, and wrote a seminal text in the field of oceanography. He died in 1905 at age 65.

Selective internal radiation therapy

Selective internal radiation therapy (SIRT), also known as transarterial radioembolization (TARE), radioembolization or intra-arterial microbrachytherapy is a form of radiation therapy used in interventional radiology to treat cancer. It is generally for selected patients with surgically unresectable cancers, especially hepatocellular carcinoma or metastasis to the liver. The treatment involves injecting tiny microspheres of radioactive material into the arteries that supply the tumor, where the spheres lodge in the small vessels of the tumor. Because this treatment combines radiotherapy with embolization, it is also called radioembolization. The chemotherapeutic analogue (combining chemotherapy with embolization) is called chemoembolization, of which transcatheter arterial chemoembolization (TACE) is the usual form.

Spin ice

A spin ice is a magnetic substance that does not have a single minimal-energy state. It has magnetic moments (i.e. "spin") as elementary degrees of freedom which are subject to frustrated interactions. By their nature, these interactions prevent the moments from exhibiting a periodic pattern in their orientation down to a temperature much below the energy scale set by the said interactions. Spin ices show low-temperature properties, residual entropy in particular, closely related to those of common crystalline water ice. The most prominent compounds with such properties are dysprosium titanate (Dy2Ti2O7) and holmium titanate (Ho2Ti2O7). The orientation of the magnetic moments in spin ice resembles the positional organization of hydrogen atoms (more accurately, ionized hydrogen, or protons) in conventional water ice (see Figure 1).

Experiments have found evidence for the existence of deconfined magnetic monopoles in these materials, with properties resembling those of the hypothetical magnetic monopoles postulated to exist in vacuum.

Thulium

Thulium is a chemical element with symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series. Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds; because it occurs so late in the series, however, the +2 oxidation state is also stabilized by the nearly full 4f shell that results. In aqueous solution, like compounds of other late lanthanides, soluble thulium compounds form coordination complexes with nine water molecules.

In 1879, the Swedish chemist Per Teodor Cleve separated from the rare earth oxide erbia another two previously unknown components, which he called holmia and thulia; these were the oxides of holmium and thulium, respectively. A relatively pure sample of thulium metal was first obtained in 1911.

Thulium is the second-least abundant of the lanthanides, after radioactively unstable promethium which is only found in trace quantities on Earth. It is an easily workable metal with a bright silvery-gray luster. It is fairly soft and slowly tarnishes in air. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices, and in some solid-state lasers. It has no significant biological role and is not particularly toxic.

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