Promethium
Encyclopedia
Promethium is a chemical element
with the symbol Pm and atomic number
61. It is notable for being the only exclusively radioactive element besides technetium
that is followed by chemical elements with stable isotopes.
in 1902. During his research on the chemical properties of rare earth element
s he found that the difference between neodymium
and samarium
is larger than between the other lanthanide
s. This prediction was supported in 1914 by Henry Moseley
who, having discovered that atomic number
was an experimentally measurable property of elements, found that no known element had atomic number 61. With the knowledge of a gap in the periodic table several groups started to search for the predicted element among other rare earths in the natural environment.
nitrate concentrate from the Brazil
ian mineral monazite
by fractionated crystallisation, they yielded a solution containing mostly samarium. This solution gave x-ray spectra attributed to samarium and element 61. In honor of their city they named element 61 Florentium. The results were published in 1926, but the scientists claimed that the experiments were done in 1924.
Also in 1926, a group of scientists from the University of Illinois at Urbana-Champaign
, Smith Hopkins and Len Yntema published the discovery of element 61. They named it illinium, after the university.
Both of these reported discoveries are now known to be erroneous because there are no stable or long-lived isotopes of promethium, hence there was none to be found in these sources.
(ORNL) in 1945 by Jacob A. Marinsky
, Lawrence E. Glendenin
and Charles D. Coryell
by separation and analysis of the fission products of uranium
fuel irradiated in the Graphite Reactor
; however, being too busy with military-related research during World War II
, they did not announce their discovery until 1947. The name promethium is derived from Prometheus
, the Titan, in Greek mythology
, who stole fire from Mount Olympus and brought it down to mankind. The name was suggested by Grace Mary Coryell, Charles Coryell's wife, who felt that they were stealing fire from the gods.
In 1963, ion-exchange methods were used at ORNL to prepare about ten grams of promethium from nuclear reactor fuel processing wastes.
Today, promethium is still recovered from the byproducts of uranium fission; it can also be produced by bombarding 146Nd with neutron
s, turning it into 147Nd which decays into 147Pm through beta decay with a half-life of 11 days.
Promethium can be formed in nature as a product of spontaneous fission
of uranium-238
and alpha decay
of europium
-151. Only trace amounts can be found in naturally occurring ores: a sample of pitchblende has been found to contain promethium at a concentration of four parts per quintillion (1018) by mass. It was calculated that the equilibrium mass of promethium in the earth's crust is about 560g due to uranium fission and about 12g due to the recently observed alpha decay of europium-151.
Promethium has also been identified in the spectrum of the star HR 465
in Andromeda
, and possibly HD 101065 (Przybylski's star
) and HD 965.
and one of two elements among the first 82 that has no stable (or even long-lived) isotopes; this is a result of a rarely occurring effect of the liquid drop model and stabilities of neighbor element isotopes. The most stable isotope of the element is promethium-145, which has a half-life of 17.7 years. In other words, if a kilogram of pure promethium-145 could be created at a moment, only about 20 grams would be left after 100 years. Promethium is also the least stable element of the first 84. The primary decay products are neodymium
and samarium
isotopes (promethium-146 decays to both, the lighter generally to neodymium, and heavier to samarium). Exact promethium isotopes may decay to praseodymium
or other promethium isotopes (in case of nuclear isomer
s).
Promethium is a lanthanide metal whose chemical properties mostly resemble those of other lanthanides. The melting point of the element was claimed to have been calculated to be around 1042 °C (1908 °F, 1315 K), well suiting in the general trend of its increase with atomic numbers in lanthanides. Pure promethium exists in two allotropic forms, and its chemistry is similar to other lanthanide
s. Promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity.
:
Promethium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form promethium hydroxide:
Promethium metal reacts with all the halogens:
Promethium(III) iodide may also be synthesized by reacting PmX3 (X = Cl, Br) with hydrogen iodide
at 400 °C:
Promethium dissolves readily in dilute sulfuric acid
to form solutions containing the pink Pm(III) ions, which exist as a [Pm(OH2)9]3+ complexes:
Promethium(III) ions form an insoluble, hygroscopic oxalate when dissolved in aqueous H2C2O4:
s during its beta decay
. It is expected to have biological toxicity comparable with beta emitters of similar half-life, for example iodine-131
. It is not as hazardous as alpha emitters such as the transuranics, due to the far lower relative biological effectiveness
of beta emitters over alpha emitters. Promethium has no biological role.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
with the symbol Pm and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
61. It is notable for being the only exclusively radioactive element besides technetium
Technetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature...
that is followed by chemical elements with stable isotopes.
Prediction
The existence of promethium was first predicted by Bohuslav BraunerBohuslav Brauner
Bohuslav Brauner was a Czech chemist.Brauner was a student of Robert Bunsen at the University of Heidelberg and later of Henry Roscoe at the University of Manchester. Brauner became lecturer for chemistry at the University of Prague in 1883 and professor in 1890...
in 1902. During his research on the chemical properties of rare earth element
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...
s he found that the difference between neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
and samarium
Samarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...
is larger than between the other lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
s. This prediction was supported in 1914 by Henry Moseley
Henry Moseley
Henry Gwyn Jeffreys Moseley was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. This stemmed from his development of Moseley's law in X-ray spectra...
who, having discovered that atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
was an experimentally measurable property of elements, found that no known element had atomic number 61. With the knowledge of a gap in the periodic table several groups started to search for the predicted element among other rare earths in the natural environment.
Florentium and Illinium
The first claim of a discovery was published by Italian scientists Luigi Rolla and Lorenzo Fernandes from Florence. After separating a didymiumDidymium
Didymium is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially when a gas powered forge is used, where it provides a filter which selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass,...
nitrate concentrate from the Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
ian mineral monazite
Monazite
Monazite is a reddish-brown phosphate mineral containing rare earth metals. It occurs usually in small isolated crystals. There are actually at least four different kinds of monazite, depending on relative elemental composition of the mineral:...
by fractionated crystallisation, they yielded a solution containing mostly samarium. This solution gave x-ray spectra attributed to samarium and element 61. In honor of their city they named element 61 Florentium. The results were published in 1926, but the scientists claimed that the experiments were done in 1924.
Also in 1926, a group of scientists from the University of Illinois at Urbana-Champaign
University of Illinois at Urbana-Champaign
The University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...
, Smith Hopkins and Len Yntema published the discovery of element 61. They named it illinium, after the university.
Both of these reported discoveries are now known to be erroneous because there are no stable or long-lived isotopes of promethium, hence there was none to be found in these sources.
True promethium
Promethium was first produced and characterized at Oak Ridge National LaboratoryOak Ridge National Laboratory
Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the DOE's largest science and energy laboratory. ORNL is located in Oak Ridge, Tennessee, near Knoxville...
(ORNL) in 1945 by Jacob A. Marinsky
Jacob A. Marinsky
Jacob Akiba Marinsky was a chemist who was the co-discoverer of the element promethium.Marinsky was born in Buffalo, New York, and attended the University at Buffalo, entering at age 16 and receiving a bachelor's degree in chemistry in 1939.During World War II he was employed as a chemist for the...
, Lawrence E. Glendenin
Lawrence E. Glendenin
Lawrence Elgin Glendenin was an American chemist who co-discovered the element promethium.- Biography :Glendenin was born in Bay City, Michigan on November 8, 1918...
and Charles D. Coryell
Charles D. Coryell
Charles DuBois Coryell was an American chemist who was one of the discoverers of the element promethium....
by separation and analysis of the fission products of uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
fuel irradiated in the Graphite Reactor
X-10 Graphite Reactor
The X-10 Graphite Reactor at Oak Ridge National Laboratory in Oak Ridge, Tennessee, formerly known as the Clinton Pile and X-10 Pile, was the world's second artificial nuclear reactor and was the first reactor designed and built for continuous operation.When President Roosevelt in December 1942...
; however, being too busy with military-related research during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, they did not announce their discovery until 1947. The name promethium is derived from Prometheus
Prometheus
In Greek mythology, Prometheus is a Titan, the son of Iapetus and Themis, and brother to Atlas, Epimetheus and Menoetius. He was a champion of mankind, known for his wily intelligence, who stole fire from Zeus and gave it to mortals...
, the Titan, in Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
, who stole fire from Mount Olympus and brought it down to mankind. The name was suggested by Grace Mary Coryell, Charles Coryell's wife, who felt that they were stealing fire from the gods.
In 1963, ion-exchange methods were used at ORNL to prepare about ten grams of promethium from nuclear reactor fuel processing wastes.
Today, promethium is still recovered from the byproducts of uranium fission; it can also be produced by bombarding 146Nd with neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s, turning it into 147Nd which decays into 147Pm through beta decay with a half-life of 11 days.
Occurrence
Spontaneous fission
Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses...
of uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...
and alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
of europium
Europium
Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard silvery metal which readily oxidizes in air and water...
-151. Only trace amounts can be found in naturally occurring ores: a sample of pitchblende has been found to contain promethium at a concentration of four parts per quintillion (1018) by mass. It was calculated that the equilibrium mass of promethium in the earth's crust is about 560g due to uranium fission and about 12g due to the recently observed alpha decay of europium-151.
Promethium has also been identified in the spectrum of the star HR 465
HR 465
GY Andromedae is an α2 Canum Venaticorum type variable star in the constellation Andromeda. Its brightness fluctuates between 6.27m and 6.41m. It belongs to the group of chemically peculiar stars...
in Andromeda
Andromeda (constellation)
Andromeda is a constellation in the northern sky. It is named after Andromeda, the princess in the Greek legend of Perseus who was chained to a rock to be eaten by the sea monster Cetus...
, and possibly HD 101065 (Przybylski's star
Przybylski's star
Przybylski's Star , or HD 101065, is a peculiar star that is located about 410 light years from the Sun in the constellation Centaurus....
) and HD 965.
Characteristics
Promethium is the only lanthanideLanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
and one of two elements among the first 82 that has no stable (or even long-lived) isotopes; this is a result of a rarely occurring effect of the liquid drop model and stabilities of neighbor element isotopes. The most stable isotope of the element is promethium-145, which has a half-life of 17.7 years. In other words, if a kilogram of pure promethium-145 could be created at a moment, only about 20 grams would be left after 100 years. Promethium is also the least stable element of the first 84. The primary decay products are neodymium
Neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite...
and samarium
Samarium
Samarium is a chemical element with the symbol Sm, atomic number 62 and atomic weight 150.36. It is a moderately hard silvery metal which readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3...
isotopes (promethium-146 decays to both, the lighter generally to neodymium, and heavier to samarium). Exact promethium isotopes may decay to praseodymium
Praseodymium
Praseodymium is a chemical element that has the symbol Pr and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating.The element...
or other promethium isotopes (in case of nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
s).
Promethium is a lanthanide metal whose chemical properties mostly resemble those of other lanthanides. The melting point of the element was claimed to have been calculated to be around 1042 °C (1908 °F, 1315 K), well suiting in the general trend of its increase with atomic numbers in lanthanides. Pure promethium exists in two allotropic forms, and its chemistry is similar to other lanthanide
Lanthanide
The lanthanide or lanthanoid series comprises the fifteen metallic chemical elements with atomic numbers 57 through 71, from lanthanum through lutetium...
s. Promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity.
Chemical properties
Promethium metals tarnish slowly in air and burns readily at 150 °C to form promethium oxidePromethium(III) oxide
Promethium oxide or promethium oxide is a compound with the formula Pm2O3. It is the most common form of promethium.-Crystal structure:Promethium oxide exists in three major crystalline forms:...
:
- 4 Pm + 3 O2 → 2 Pm2O3
Promethium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form promethium hydroxide:
- 2 Pm (s) + 6 H2O (l) → 2 Pm(OH)3 (aq) + 3 H2 (g)
Promethium metal reacts with all the halogens:
- 2 Pm (s) + 3 F2 (g) → 2 PmF3 (s)
- 2 Pm (s) + 3 Cl2 (g) → 2 PmCl3 (s)
- 2 Pm (s) + 3 Br2 (g) → 2 PmBr3 (s)
- 2 Pm (s) + 3 I2 (g) → 2 PmI3 (s)
Promethium(III) iodide may also be synthesized by reacting PmX3 (X = Cl, Br) with hydrogen iodide
Hydrogen iodide
Hydrogen iodide is a diatomic molecule. Aqueous solutions of HI are known as iohydroic acid or hydroiodic acid, a strong acid. Gas and aqueous solution are interconvertible...
at 400 °C:
- 2 PmX3(s) + 3HI(g) → PmI3(s) + 3HX(g)
Promethium dissolves readily in dilute sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
to form solutions containing the pink Pm(III) ions, which exist as a [Pm(OH2)9]3+ complexes:
- 2 Pm(s) + 3 H2SO4 (aq) → 2 Pm3+ (aq) + 3 (SO4)2- (aq) + 3 H2 (g)
Promethium(III) ions form an insoluble, hygroscopic oxalate when dissolved in aqueous H2C2O4:
- 2 Pm3+(aq) + C2O42- (aq) → Pm2(C2O4)3•xH2O(s)
Applications
Uses for promethium include:- As a beta radiation source for thickness gauges.
- As a light source for signals that require reliable, independent operation (using phosphorPhosphorA phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
to absorb the beta radiation and produce light). In particular, Promethium(III) chloride (PmCl3) mixed with zinc sulfideZinc sulfideZinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...
(ZnZincZinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
SSulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
) was used for a time as a major luminous paint for watches after radiumRadiumRadium is a chemical element with atomic number 88, represented by the symbol Ra. Radium is an almost pure-white alkaline earth metal, but it readily oxidizes on exposure to air, becoming black in color. All isotopes of radium are highly radioactive, with the most stable isotope being radium-226,...
was discontinued. This mixture is still occasionally used for some luminous paint applications (though most such uses requiring radioactive materials have switched to tritiumTritiumTritium is a radioactive isotope of hydrogen. The nucleus of tritium contains one proton and two neutrons, whereas the nucleus of protium contains one proton and no neutrons...
for safety reasons). - In an atomic batteryAtomic batteryThe terms atomic battery, nuclear battery, tritium battery and radioisotope generator are used to describe a device which uses the emissions from a radioactive isotope to generate electricity. Like nuclear reactors they generate electricity from atomic energy, but differ in that they do not use a...
in which cells convert the beta emissions into electric current, yielding a useful life of about five years, using Pm-147. - Promethium has possible future uses in portable X-ray sources, and as auxiliary heat or power sources for space probes and satellites (although the alpha emitter plutonium-238Plutonium-238-External links:**...
has become standard for most space-exploration related uses – see Radioisotope thermoelectric generators).
Precautions
Promethium must be handled with great care because of its high radioactivity. In particular, promethium can emit X-rayX-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s during its beta decay
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
. It is expected to have biological toxicity comparable with beta emitters of similar half-life, for example iodine-131
Iodine-131
Iodine-131 , also called radioiodine , is an important radioisotope of iodine. It has a radioactive decay half-life of about eight days. Its uses are mostly medical and pharmaceutical...
. It is not as hazardous as alpha emitters such as the transuranics, due to the far lower relative biological effectiveness
Relative biological effectiveness
In radiology, the relative biological effectiveness is a number that expresses the relative amount of damage that a fixed amount of ionizing radiation of a given type can inflict on biological tissues...
of beta emitters over alpha emitters. Promethium has no biological role.
Compounds
Promethium compounds include:- Chlorides
- PmCl3 (lavender)
- Bromides
- PmBr3 (coral - red)
- Fluorides
- PmF3 (purple - pink)
- Nitrates
- Pm(NO3)3
- Oxalates
- Pm2(C2O4)3
- Oxides
- Pm2O3Promethium(III) oxidePromethium oxide or promethium oxide is a compound with the formula Pm2O3. It is the most common form of promethium.-Crystal structure:Promethium oxide exists in three major crystalline forms:...
- Pm2O3