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{{infobox promethium|image name=Promethium.gif}} 
'''Promethium''' is a [[chemical element]] with [[Symbol (chemistry)|symbol]] '''Pm''' and [[atomic number]] 61. All of its [[isotope]]s are [[Radioactive decay|radioactive]]; it is extremely rare, with only about 500–600 grams naturally occurring in the Earth's crust at any given time. Promethium is one of the only two radioactive elements that are both preceded and followed in the [[periodic table]] by elements with stable forms, the other being [[technetium]]. Chemically, promethium is a [[lanthanide]]. Promethium shows only one stable [[oxidation state]] of +3.

In 1902 [[Bohuslav Brauner]] suggested that there was a then-unknown element with properties intermediate between those of the known elements [[neodymium]] (60) and [[samarium]] (62); this was confirmed in 1914 by [[Henry Moseley]], who, having measured the atomic numbers of all the elements then known, found that the element with atomic number 61 was missing. In 1926, two groups (one Italian and one American) claimed to have isolated a sample of element 61; both "discoveries" were soon proven to be false. In 1938, during a nuclear experiment conducted at [[Ohio State University]]<!--Wikipedians do not use "The" as part of Ohio State's name; it is considered a marketing gimmick, and routinely deleted.-->, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not much recognized. Promethium was first produced and characterized at [[Oak Ridge National Laboratory]] in 1945 by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. The discoverers proposed the name "prometheum" (the spelling was subsequently changed), derived from [[Prometheus]], the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans, to symbolize "both the daring and the possible misuse of mankind's intellect". A sample of the metal was made only in 1963.

The two sources of natural promethium are rare [[alpha decay]]s of natural [[europium]]-151 (producing promethium-147) and [[spontaneous fission]] of [[uranium]] (various isotopes). Promethium-145 is the most stable promethium isotope, but the only isotope with practical applications is promethium-147, chemical compounds of which are used in [[luminous paint]], [[atomic battery|atomic batteries]] and thickness-measurement devices. Because natural promethium is exceedingly scarce, it is typically synthesized by bombarding uranium-235 ([[enriched uranium]]) with [[thermal neutron]]s to produce promethium-147 as a [[fission product]].

==Properties==

===Physical properties===
A promethium atom has 61 electrons, arranged in the [[electron configuration|configuration]] &#91;[[xenon|Xe]]&#93;&nbsp;4f<sup>5</sup>&nbsp;6s<sup>2</sup>. The seven 4f and 6s electrons are [[valence electron|valence]] electrons.<ref name="Cotton">{{Greenwood&Earnshaw|page=1233}}</ref> In forming compounds, the atom loses its two outermost electrons and one 4f-electron, which belongs to an open subshell. The element's atomic radius is the second largest among all the lanthanides but is only slightly greater than those of the neighboring elements.<ref name="Cotton" /> It is the most notable exception to the general trend of the contraction of lanthanide atoms with the increase of their atomic numbers ([[lanthanide contraction]]<ref>{{Cotton&Wilkinson5th|pages=776, 955}}</ref>). Many properties of promethium rely on its position among lanthanides and are intermediate between those of neodymium and samarium. For example, the melting point, the first three ionization energies, and the hydration energy are greater than those of neodymium and lower than those of samarium;<ref name="Cotton" /> similarly, the estimate for the boiling point, ionic (Pm<sup>3+</sup>) radius, and standard heat of formation of monatomic gas are greater than those of samarium and less than those of neodymium.<ref name="Cotton" />

Promethium has a [[Close-packing of equal spheres|double hexagonal close packed]] (dhcp) structure and a hardness of 63&nbsp;kg/mm<sup>2</sup>.<ref name="str" /> This low-temperature alpha form converts into a beta, [[Cubic crystal system|body-centered cubic]] (bcc) phase upon heating to 890&nbsp;°C.<ref name="CRCrare" />

===Chemical properties and compounds===
[[File:Promethium-147 solution.jpg|thumb|150px|Solution containing Pm<sup>3+</sup> ions]]
Promethium belongs to the [[cerium group]] of lanthanides and is chemically very similar to the neighboring elements.{{sfn|Lavrukhina|Pozdnyakov|1966|p=120}} Because of its instability, chemical studies of promethium are incomplete. Even though a few compounds have been synthesized, they are not fully studied; in general, they tend to be pink or red in color.{{sfn|Emsley|2011|p=429}}<ref name="brit">[http://www.britannica.com/EBchecked/topic/478714/promethium promethium]. Encyclopædia Britannica Online</ref> In May 2024, a promethium coordination complex with neutral PyDGA ligands was characterized in aqueous solution.<ref>{{Cite journal |last1=Driscoll |first1=Darren M. |last2=White |first2=Frankie D. |last3=Pramanik |first3=Subhamay |last4=Einkauf |first4=Jeffrey D. |last5=Ravel |first5=Bruce |last6=Bykov |first6=Dmytro |last7=Roy |first7=Santanu |last8=Mayes |first8=Richard T. |last9=Delmau |first9=Lætitia H. |last10=Cary |first10=Samantha K. |last11=Dyke |first11=Thomas |last12=Miller |first12=April |last13=Silveira |first13=Matt |last14=VanCleve |first14=Shelley M. |last15=Davern |first15=Sandra M. |date=May 2024 |title=Observation of a promethium complex in solution |journal=Nature |language=en |volume=629 |issue=8013 |pages=819–823 |doi=10.1038/s41586-024-07267-6 |pmid=38778232 |issn=1476-4687|pmc=11111410 |bibcode=2024Natur.629..819D }}</ref> Treatment of acidic solutions containing {{chem2|Pm(3+)}} ions with [[ammonia]] results in a gelatinous light-brown sediment of hydroxide, {{chem2|Pm(OH)3}}, which is insoluble in water.{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} When dissolved in [[hydrochloric acid]], a water-soluble yellow salt, {{chem2|PmCl3}}, is produced;{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} similarly, when dissolved in nitric acid, a nitrate results, {{chem2|Pm(NO3)3}}. The latter is also well-soluble; when dried, it forms pink crystals, similar to {{chem2|Nd(NO3)3}}.{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} The electron configuration for {{chem2|Pm(3+)}} is [Xe] 4f<sup>4</sup>, and the color of the ion is pink. The ground state term symbol is <sup>5</sup>I<sub>4</sub>.<ref>{{cite book|title=Chemistry of the f-block elements| author=Aspinall, H. C.|year= 2001| page=34, Table 2.1|publisher=Gordon & Breach|isbn=978-9056993337}}</ref> The sulfate is slightly soluble, like the other cerium group sulfates. Cell parameters have been calculated for its octahydrate; they lead to conclusion that the density of {{chem2|Pm2(SO4)3*8H2O}} is 2.86&nbsp;g/cm<sup>3</sup>.{{sfn|Lavrukhina|Pozdnyakov|1966|p=122}} The oxalate, {{chem2|Pm2(C2O4)3*10H2O}}, has the lowest solubility of all lanthanide oxalates.{{sfn|Lavrukhina|Pozdnyakov|1966|p=123}}

Unlike the nitrate, the [[promethium oxide|oxide]] is similar to the corresponding samarium salt and not the neodymium salt. As-synthesized, e.g. by heating the oxalate, it is a white or lavender-colored powder with disordered structure.{{sfn|Lavrukhina|Pozdnyakov|1966|p=121}} This powder crystallizes in a cubic lattice upon heating to 600&nbsp;°C. Further annealing at 800&nbsp;°C and then at 1750&nbsp;°C irreversibly transforms it to [[monoclinic]] and [[Hexagonal crystal system|hexagonal]] phases, respectively, and the last two phases can be interconverted by adjusting the annealing time and temperature.<ref name="PmO" />

{| Class = "wikitable" style = "text-align: center"
! Formula
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! ''a'' (pm)
! ''b'' (pm)
! ''c'' (pm)
! ''Z''
! density, <br/>g/cm<sup>3</sup>
|-
| α-Pm
| [[Close-packing of equal spheres|dhcp]]<ref name="str">{{cite journal|doi=10.1016/0022-5088(71)90101-9|title=The crystal structure of promethium|year=1971|last1=Pallmer|first1=P. G.|last2=Chikalla|first2=T. D.|journal=Journal of the Less Common Metals|volume=24|issue=3|pages=233| issn = 0022-5088}}</ref><ref name="CRCrare">{{cite book |editor=Lide, D. R. |author=Gschneidner Jr., K.A. |chapter=Physical Properties of the rare earth metals |title=CRC Handbook of Chemistry and Physics |edition=86th |location=Boca Raton, FL |publisher=CRC Press |year=2005 |isbn=978-0-8493-0486-6 |chapter-url=http://203.158.253.140/media/e-Book/Engineer/Chemistry/Handbook%20of%20Chemistry%20and%20Physics/Section%2004/04_03_86.pdf |access-date=2012-06-20 |archive-url=https://www.webcitation.org/6AlZkPuDd?url=http://203.158.253.140/media/e-Book/Engineer/Chemistry/Handbook%20of%20Chemistry%20and%20Physics/Section%2004/04_03_86.pdf |archive-date=2012-09-18 |url-status=dead }}</ref>
| P6<sub>3</sub>/mmc
| 194
| hP4
| 365
| 365
| 1165
| 4
| 7.26
|-
| β-Pm
| [[Cubic crystal system|bcc]]<ref name="CRCrare" />
| Fm{{overline|3}}m
| 225
| cF4
| 410
| 410
| 410
| 4
| 6.99
|-
| Pm<sub>2</sub>O<sub>3</sub>
| cubic<ref name="PmO" />
| Ia{{overline|3}}
| 206
| cI80
| 1099
| 1099
| 1099
| 16
| 6.77
|-
| Pm<sub>2</sub>O<sub>3</sub>
| monoclinic<ref name="PmO">{{cite journal|doi=10.1111/j.1151-2916.1972.tb11329.x|title=Polymorphic Modifications of Pm2O3|year=1972|last1=Chikalla|first1=T. D.|last2=McNeilly|first2=C. E.|last3=Roberts|first3=F. P.|journal=Journal of the American Ceramic Society|volume=55|issue=8|pages=428}}</ref>
| C2/m
| 12
| mS30
| 1422
| 365
| 891
| 6
| 7.40
|-
| Pm<sub>2</sub>O<sub>3</sub>
| hexagonal<ref name="PmO" />
| P{{overline|3}}m1
| 164
| hP5
| 380.2
| 380.2
| 595.4
| 1
| 7.53
|}

Promethium forms only one stable oxidation state, +3, in the form of ions; this is in line with other lanthanides. Promethium can also form the +2 oxidation state.<ref>{{Holleman&Wiberg|page=1704}}</ref> Thermodynamic properties of Pm<sup>2+</sup> suggests that the dihalides are stable, similar to NdCl<sub>2</sub> and SmCl<sub>2</sub>.<ref>{{cite journal | last1=Elkina | first1=Veronika | last2=Kurushkin | first2=Mikhail | title=Promethium: To Strive, to Seek, to Find and Not to Yield | journal=Frontiers in Chemistry | volume=8 | date=2020-07-10 | page=588 | issn=2296-2646 | doi=10.3389/fchem.2020.00588 | doi-access=free| pmid=32754576 | pmc=7366832 | bibcode=2020FrCh....8..588E }}</ref>

{| Class = "wikitable" style = "text-align: center"
|+Promethium halides<ref>{{cite book|author=Cotton, Simon|title=Lanthanide And Actinide Chemistry|url=https://books.google.com/books?id=SvAbtU6XvzgC&pg=PA117|year= 2006|publisher=John Wiley & Sons|isbn=978-0-470-01006-8|page=117}}</ref>
! Formula
! color
! coordination<br/>number
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! [[melting point|m.p.]] (°C)
|-
|PmF<sub>3</sub>
|Purple-pink
|11
|hexagonal
|P{{overline|3}}c1
|165
|hP24
|1338
|-
|PmCl<sub>3</sub>
|Lavender
|9
|hexagonal
|P6<sub>3</sub>/mc
|176
|hP8
|655
|-
|PmBr<sub>3</sub>
|Red
|8
|orthorhombic
|Cmcm
|63
|oS16
|624
|-
|α-PmI<sub>3</sub>
|Red
|8
|orthorhombic
|Cmcm
|63
|oS16
|α→β
|-
|β-PmI<sub>3</sub>
|Red
|6
|rhombohedral
|R{{overline|3}}
|148
|hR24
|695
|}

===Isotopes===
{{Main|Isotopes of promethium}}
Promethium is the only [[lanthanide]] and one of only two elements among the first 82 with no stable or long-lived ([[primordial isotope|primordial]]) isotopes. This is a result of a [[Isotopes of technetium#Stability of technetium isotopes|rarely occurring effect]] of the [[liquid drop model]] and stabilities of neighbor element isotopes; it is also the least stable element of the first 84.{{NUBASE2020|ref}} The primary decay products are [[neodymium]] and [[samarium]] isotopes (promethium-146 decays to both, the lighter isotopes generally to neodymium via [[positron decay]] and [[electron capture]], and the heavier isotopes to samarium via beta decay). Promethium [[nuclear isomer]]s may decay to other promethium isotopes and one isotope (<sup>145</sup>Pm) has a very rare alpha decay mode to stable [[praseodymium]]-141.{{NUBASE2020|ref}}

The most stable isotope of the element is promethium-145, which has a specific activity of {{convert|139|Ci/g|TBq/g|abbr=on|lk=on}} and a half-life of 17.7&nbsp;years via [[electron capture]].{{NUBASE2020|ref}}<ref name="CRCel" /> Because it has 84 neutrons (two more than 82, which is a [[magic number (physics)|magic number]] which corresponds to a stable neutron configuration), it may emit an [[alpha particle]] (which has 2 neutrons) to form praseodymium-141 with 82 neutrons. Thus it is the only promethium isotope with an experimentally observed [[alpha decay]].{{sfn|Lavrukhina|Pozdnyakov|1966|p=114}} Its [[partial half-life]] for alpha decay is about 6.3{{e|9}}&nbsp;years, and the relative probability for a <sup>145</sup>Pm nucleus to decay in this way is 2.8{{e|-7}}&nbsp;%. Several other promethium isotopes such as <sup>144</sup>Pm, <sup>146</sup>Pm, and <sup>147</sup>Pm also have a positive energy release for alpha decay; their alpha decays are predicted to occur but have not been observed. In total, 41 isotopes of promethium are known, ranging from <sup>126</sup>Pm to <sup>166</sup>Pm.{{NUBASE2020|ref}}<ref name=Ln922>{{cite journal |last1=Kiss |first1=G. G. |last2=Vitéz-Sveiczer |first2=A. |last3=Saito |first3=Y. |display-authors=et al. |title=Measuring the β-decay properties of neutron-rich exotic Pm, Sm, Eu, and Gd isotopes to constrain the nucleosynthesis yields in the rare-earth region |journal=The Astrophysical Journal |volume=936 |issue=107 |date=2022 |page=107 |doi=10.3847/1538-4357/ac80fc|bibcode=2022ApJ...936..107K |s2cid=252108123 |hdl=2117/375253 |hdl-access=free |doi-access=free }}</ref>

The element also has 18 nuclear isomers, with [[mass number]]s of 133 to 142, 144, 148, 149, 152, and 154 (some mass numbers have more than one isomer). The most stable of them is promethium-148m, with a half-life of 43.1&nbsp;days; this is longer than the half-lives of the ground states of all promethium isotopes, except for promethium-143 to 147. In fact, promethium-148m has a longer half-life than its ground state, promethium-148.{{NUBASE2020|ref}}

==Occurrence==
[[File:Pitchblende schlema-alberoda.JPG|left|thumb|[[Uraninite]], a uranium ore and the host for most of Earth's promethium ]]
In 1934, [[Willard Libby]] reported that he had found weak beta activity in pure neodymium, which was attributed to a half-life over 10<sup>12</sup>&nbsp;years.{{sfn|Lavrukhina|Pozdnyakov|1966|p=117}} Almost 20 years later, it was claimed that the element occurs in natural neodymium in equilibrium in quantities below 10<sup>−20</sup> grams of promethium per one gram of neodymium.{{sfn|Lavrukhina|Pozdnyakov|1966|p=117}} However, these observations were disproved by newer investigations, because for all seven naturally occurring neodymium isotopes, any single beta decays (which can produce promethium isotopes) are forbidden by energy conservation.<ref>{{cite journal |author1=G. Audi |author2=A. H. Wapstra |author3=C. Thibault |author4=J. Blachot |author5=O. Bersillon |year=2003 |title=The NUBASE evaluation of nuclear and decay properties |url=http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf |journal=[[Nuclear Physics A]] |volume=729 |issue=1 |pages=3–128 |doi=10.1016/j.nuclphysa.2003.11.001 |bibcode=2003NuPhA.729....3A |url-status=dead |archive-url=https://web.archive.org/web/20080923135135/http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf |archive-date=2008-09-23 |citeseerx=10.1.1.692.8504 }}</ref> In particular, careful measurements of atomic masses show that the mass difference between <sup>150</sup>Nd and <sup>150</sup>Pm is negative (−87&nbsp;keV), which absolutely prevents the single beta decay of <sup>150</sup>Nd to <sup>150</sup>Pm.<ref>{{cite book |author=N. E. Holden |year=2004 |editor=D. R. Lide |chapter=Table of the Isotopes |title=CRC Handbook of Chemistry and Physics |page=[https://archive.org/details/crchandbookofche81lide/page/ Section 11] |no-pp=yes |edition=85th |publisher=[[CRC Press]] |isbn=978-0-8493-0485-9 |title-link=CRC Handbook of Chemistry and Physics }}</ref>

In 1965, [[Olavi Erämetsä]] separated out traces of <sup>147</sup>Pm from a rare earth concentrate purified from [[apatite]], resulting in an upper limit of 10<sup>−21</sup> for the abundance of promethium in nature; this may have been produced by the natural nuclear fission of uranium, or by [[cosmic ray spallation]] of <sup>146</sup>Nd.<ref>{{Ullmann|volume=31|page=188|last1=McGill|first1=Ian|contribution=Rare Earth Elements|doi=10.1002/14356007.a22_607}}</ref>

Both isotopes of natural europium have larger [[mass excess]]es than sums of those of their potential alpha daughters plus that of an alpha particle; therefore, they (stable in practice) may alpha decay to promethium.<ref name="Mammamia" /> Research at [[Laboratori Nazionali del Gran Sasso]] showed that europium-151 decays to promethium-147 with the half-life of 5{{e|18}}&nbsp;years.<ref name="Mammamia" /> It has been shown that europium is "responsible" for about 12&nbsp;grams of promethium in the Earth's crust.<ref name="Mammamia" /> Alpha decays for europium-153 have not been found yet, and its theoretically calculated half-life is so high (due to low energy of decay) that this process will probably not be observed in the near future.<ref name="bellidecay">{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |display-authors=3 |title=Experimental searches for rare alpha and beta decays |journal=European Physical Journal A |date=2019 |volume=55 |issue=8 |pages=140–1–140–7 |doi=10.1140/epja/i2019-12823-2 |issn=1434-601X |arxiv=1908.11458|bibcode=2019EPJA...55..140B |s2cid=201664098 }}</ref>

Promethium can also be formed in nature as a product of [[spontaneous fission]] of [[uranium-238]].{{sfn|Lavrukhina|Pozdnyakov|1966|p=117}} 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 (4{{e|-18}}) by mass.<ref>{{cite journal |author1=Attrep, Moses Jr. |author2=Kuroda, P. K. |name-list-style=amp |date=May 1968 |title=Promethium in pitchblende |journal=Journal of Inorganic and Nuclear Chemistry |volume=30 |issue=3 |pages=699–703 |doi=10.1016/0022-1902(68)80427-0}}</ref> Uranium is thus "responsible" for 560&nbsp;g of promethium in [[Earth's crust]].<ref name="Mammamia">{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Cappella |first3=F. |last4=Cerulli |first4=R. |last5=Dai |first5=C. J. |last6=Danevich |first6=F. A. |last7=D'Angelo |first7=A. |last8=Incicchitti |first8=A. |last9=Kobychev |first9=V. V. |title=Search for α decay of natural Europium |year=2007 |journal=Nuclear Physics A |volume=789 |issue=1–4 |pages=15–29 |doi=10.1016/j.nuclphysa.2007.03.001 |bibcode=2007NuPhA.789...15B |display-authors=3}}</ref>

Promethium has also been identified in the spectrum of the star [[HR 465]] in [[Andromeda (constellation)|Andromeda]]; it also has been found in HD 101065 ([[Przybylski's star]]) and HD 965.<ref>{{cite journal|author1=C. R. Cowley |author2=W. P. Bidelman |author3=S. Hubrig |author4=G. Mathys |author5=D. J. Bord |name-list-style=amp |year = 2004|title = On the possible presence of promethium in the spectra of HD 101065 (Przybylski's star) and HD 965|journal = Astronomy & Astrophysics|volume = 419|pages = 1087–1093|doi = 10.1051/0004-6361:20035726|bibcode=2004A&A...419.1087C|issue = 3|doi-access=free}}</ref> Because of the short half-life of promethium isotopes, they should be formed near the surface of those stars.<ref name="CRCel">{{cite book | editor= Haynes, William M. | year = 2011 | title = CRC Handbook of Chemistry and Physics | edition = 92nd | publisher = [[CRC Press]] | isbn = 978-1439855119|page=4.28|chapter=Prometium in "The Elements"|author=Hammond, C. R.| title-link = CRC Handbook of Chemistry and Physics }}</ref>

==History==

===Searches for element 61===
In 1902, Czech chemist [[Bohuslav Brauner]] found out that the differences in properties between neodymium and samarium were the largest between any two consecutive lanthanides in the sequence then known; as a conclusion, he suggested there was an element with intermediate properties between them.<ref name="61a">{{cite journal|title =A Revised Periodic Table: With the Lanthanides Repositioned|journal=Foundations of Chemistry|volume=7|issue=3|year=2005|doi=10.1007/s10698-004-5959-9|pages=203–233|first=Michael|last=Laing|s2cid=97792365}}</ref> This prediction was supported in 1914 by [[Henry Moseley]] who, having discovered that [[atomic number]] was an experimentally measurable property of elements, found that a few atomic numbers had no known corresponding elements: the gaps were 43, 61, 72, 75, 85, and 87.<ref>{{cite book|title=Atomic and Nuclear Physics: An Introduction in S.I. Units|edition=2nd|year=1968|publisher=Van Nostrand|page=109|last1=Littlefield |first1=Thomas Albert|last2=Thorley|first2=Norman}}</ref> 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.{{sfn|Lavrukhina|Pozdnyakov|1966|p=108}}<ref name="Weeks">{{cite book |last1=Weeks |first1=Mary Elvira |title=The discovery of the elements |date=1956 |publisher=Journal of Chemical Education |location=Easton, PA |url=https://archive.org/details/discoveryoftheel002045mbp |edition=6th }}</ref><ref name="Marshall">{{cite journal |last1=Marshall |first1=James L. Marshall |last2=Marshall |first2=Virginia R. Marshall |title=Rediscovery of the elements: The Rare Earths–The Last Member |journal=The Hexagon |date=2016 |pages=4–9 |url=https://chemistry.unt.edu/sites/default/files/users/owj0001/rare%20earths%20III_0.pdf |access-date=30 December 2019 |archive-date=27 November 2021 |archive-url=https://web.archive.org/web/20211127115101/https://chemistry.unt.edu/sites/default/files/users/owj0001/rare%20earths%20III_0.pdf |url-status=dead }}</ref>

The first claim of a discovery was published by Luigi Rolla and Lorenzo Fernandes of [[Florence]], Italy. After separating a mixture of a few rare earth elements nitrate concentrate from the [[Brazil]]ian mineral [[monazite]] by fractionated crystallization, 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.<ref>{{cite journal|doi=10.1002/zaac.19261570129|title=Über das Element der Atomnummer 61|year=1926|last1=Rolla|first1=Luigi|last2=Fernandes|first2=Lorenzo|journal=Zeitschrift für Anorganische und Allgemeine Chemie|volume=157|pages=371–381|language=de}}</ref><ref>{{cite journal|doi=10.1038/120014c0|title=Florentium or Illinium?|year=1927|author=Noyes, W. A.|journal=Nature |volume=120|pages=14|issue=3009|bibcode=1927Natur.120...14N|s2cid=4094131|doi-access=free}}</ref><ref>{{cite journal|doi=10.1038/119637a0|title=Florentium or Illinium?|year=1927|author=Rolla, L.|journal=Nature |volume=119|pages=637|last2=Fernandes|first2=L.|issue=3000|bibcode=1927Natur.119..637R|s2cid=4127574}}</ref><ref>{{cite journal|doi=10.1002/zaac.19281690128|title=Florentium. II|year=1928 |author=Rolla, Luigi|journal=Zeitschrift für Anorganische und Allgemeine Chemie|volume=169|pages=319–320|last2=Fernandes|first2=Lorenzo}}</ref><ref>{{cite journal |doi=10.1002/zaac.19271630104|title=Florentium|year=1927|author=Rolla, Luigi|journal=Zeitschrift für Anorganische und Allgemeine Chemie|volume=163 |pages=40–42|last2=Fernandes |first2=Lorenzo}}</ref><ref>{{cite journal|doi=10.1002/zaac.19271600119|title=Über Das Element der Atomnummer 61 (Florentium)|year=1927|author=Rolla, Luigi|journal=Zeitschrift für Anorganische und Allgemeine Chemie|volume=160|pages=190–192|last2=Fernandes|first2=Lorenzo}}</ref> 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.<ref>{{cite journal |doi=10.1038/117792a0|title=The Element of Atomic Number 61; Illinium|year=1926|author=Harris, J. A.|journal=Nature|volume=117|pages=792|last2=Yntema|first2=L. F.|last3=Hopkins|first3=B. S.|issue=2953 |bibcode=1926Natur.117..792H|doi-access=free}}</ref><ref>{{cite journal|doi=10.1038/118084b0|title=The New Element of Atomic Number 61: Illinium|year=1926|author=Brauner, Bohuslav |journal=Nature|volume=118|pages=84–85|issue=2959|bibcode=1926Natur.118...84B|s2cid=4089909}}</ref><ref>{{cite journal|doi=10.1007/BF01490264|title=Über das Element 61 (Illinium)|year=1926 |author=Meyer, R. J.|journal=Naturwissenschaften|volume=14|pages=771|last2=Schumacher|first2=G.|last3=Kotowski|first3=A.|bibcode=1926NW.....14..771M|issue=33|s2cid=46235121}}</ref> Both of these reported discoveries were shown to be erroneous because the spectrum line that "corresponded" to element 61 was identical to that of [[didymium]]; the lines thought to belong to element 61 turned out to belong to a few impurities (barium, chromium, and platinum).{{sfn|Lavrukhina|Pozdnyakov|1966|p=108}}

<!----REFS!!!--->In 1934, [[Josef Mattauch]] finally formulated the [[Mattauch isobar rule|isobar rule]]. One of the indirect consequences of this rule was that element 61 was unable to form stable isotopes.{{sfn|Lavrukhina|Pozdnyakov|1966|p=108}}<ref name="rare-earth-handbook">{{cite book|last1=Thyssen|first1=Pieter|last2=Binnemans|first2=Koen|editor1-last=Gschneider|editor1-first=Karl A. Jr.|editor2-last=Bünzli|editor2-first=Jean-Claude|editor3-last=Pecharsky|editor3-first=Vitalij K.|chapter=Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis|title=Handbook on the Physics and Chemistry of Rare Earths|year=2011|page=63|publisher=Elsevier|location=Amsterdam|isbn=978-0-444-53590-0|oclc=690920513|chapter-url=https://books.google.com/books?id=8SstnPFSzb0C&pg=PA66|access-date=2013-04-25}}</ref> From 1938, a nuclear experiment was conducted by H. B. Law et al. at the [[Ohio State University]]. Nuclides were produced in 1941 which were not radioisotopes of neodymium or samarium, and the name "cyclonium" was proposed, but there was a lack of chemical proof that element 61 was produced and the discovery was not largely recognized.{{sfn|Emsley|2011|p=428}}<ref>{{cite book |first1=Marco |last1=Fontani |first2=Mariagrazia |last2=Costa |first3=Mary Virginia |last3=Orna |trans-title=The Periodic Table's Shadow Side |title=The Lost Elements |publisher=Oxford University Press |place=New York |year=2015 |orig-year=2014 |isbn=978-0-19-938334-4 |pages=302–303}}</ref>

===Discovery and synthesis of promethium metal===
Promethium was first produced and characterized at [[Oak Ridge National Laboratory]] (Clinton Laboratories at that time) 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 [[X-10 Graphite Reactor|graphite reactor]]; however, being too busy with military-related research during [[World War II]], they did not announce their discovery until 1947.<ref name="Marinsky">{{cite journal |doi=10.1021/ja01203a059 |year=1947 |last1=Marinsky |first1=J. A. |last2=Glendenin |first2=L. E. |last3=Coryell |first3=C. D. |journal=Journal of the American Chemical Society |volume=69 |issue=11 |pages=2781–5 |pmid=20270831 |title=The chemical identification of radioisotopes of neodymium and of element 61|bibcode=1947JAChS..69.2781M |hdl=2027/mdp.39015086506477 |hdl-access=free }}</ref><ref>{{cite journal |year=2003 |title=Discovery of Promethium |journal=Oak Ridge National Laboratory Review |volume=36 |issue=1 |url= http://www.ornl.gov/info/ornlreview/v36_1_03/article_02.shtml |access-date=2006-09-17 |url-status=dead |archive-url= https://web.archive.org/web/20150706071605/http://www.ornl.gov/info/ornlreview/v36_1_03/article_02.shtml |archive-date=2015-07-06}}<br />{{cite journal |year=2003 |title=Discovery of Promethium |journal=Oak Ridge National Laboratory Review |volume=36 |issue=1 |page=3 |url=https://www.ornl.gov/sites/default/files/ORNL%20Review%20v36n1%202003.pdf#page=5 |access-date=2018-06-17}}</ref> The original proposed name was "clintonium", after the laboratory where the work was conducted; however, the name "prometheum" was suggested by Grace Mary Coryell, the wife of one of the discoverers.{{sfn|Emsley|2011|p=428}} It is derived from [[Prometheus]], the Titan in [[Greek mythology]] who stole fire from Mount Olympus and brought it down to humans{{sfn|Emsley|2011|p=428}} and symbolizes "both the daring and the possible misuse of the mankind intellect".<ref>{{cite book|title=Inorganic Chemistry|publisher=John Wiley and Sons|page=1694|first1=Egon|last1=Wiberg|first2=Nils|last2=Wiberg |first3=Arnold Frederick|last3=Holleman|year=2001|isbn=978-0-12-352651-9}}</ref> The spelling was then changed to "promethium", as this was in accordance with most other metals.{{sfn|Emsley|2011|p=428}}

<gallery widths="180" heights="200" class="center">
  File:Jacob A Marinsky.jpg|[[Jacob A. Marinsky]]
  File:Larry E Glendenin.jpg|[[Lawrence E. Glendenin]]
  File:Charles D. Coryell M.I.T. May 1947.png|[[Charles D. Coryell]]
</gallery>

In 1963, promethium(III) fluoride was used to make promethium metal. Provisionally purified from impurities of samarium, neodymium, and americium, it was put into a [[tantalum]] crucible which was located in another tantalum crucible; the outer crucible contained lithium metal (10 times excess compared to promethium).{{sfn|Emsley|2011|p=429}}{{sfn|Lavrukhina|Pozdnyakov|1966|p=123}} After creating a vacuum, the chemicals were mixed to produce promethium metal:

:PmF<sub>3</sub> + 3&nbsp;Li → Pm + 3&nbsp;LiF

The promethium sample produced was used to measure a few of the metal's properties, such as its [[melting point]].{{sfn|Lavrukhina|Pozdnyakov|1966|p=123}}

In 1963, ion-exchange methods were used at ORNL to prepare about ten grams of promethium from nuclear reactor fuel processing wastes.<ref name="CRCel" /><ref>{{cite journal|doi =10.1007/BF02037697|title =Chemical study on the separation and purification of promethium-147|year =1989|author =Lee, Chung-Sin|journal =Journal of Radioanalytical and Nuclear Chemistry|volume =130|pages =21–37|last2 =Wang|first2 =Yun-Ming|last3 =Cheng|first3 =Wu-Long|last4 =Ting|first4 =Gann|issue =1|bibcode =1989JRNC..130...21L|s2cid =96599441}}</ref><ref>{{cite web |url= http://www.ornl.gov/info/reports/1962/3445605484259.pdf |title= Ion exchange purification of promethium-147 and its separation from americium-241, with diethylenetriaminepenta-acetic acid as the eluant |author= Orr, P. B. |publisher= Oak Ridge National Laboratory |year= 1962 |access-date= 2011-01-31 |archive-url= https://web.archive.org/web/20110629124017/http://www.ornl.gov/info/reports/1962/3445605484259.pdf |archive-date= 2011-06-29 |url-status= dead }}<br />{{cite report |url=https://www.osti.gov/servlets/purl/4819080/ |title=Ion exchange purification of promethium-147 and its separation from americium-241, with diethylenetriaminepenta-acetic acid as the eluant |author=Orr, P. B. |publisher=Oak Ridge National Laboratory |year=1962 |doi=10.2172/4819080 |access-date=2018-06-17 |hdl=2027/mdp.39015077313933 |osti=4819080 |hdl-access=free }}</ref>

Promethium can be either recovered from the byproducts of uranium fission or produced by bombarding <sup>146</sup>Nd with [[neutron]]s, turning it into <sup>147</sup>Nd, which decays into [[promethium-147|<sup>147</sup>Pm]] through beta decay with a half-life of 11 days.<ref>{{cite web|url=http://education.jlab.org/itselemental/ele061.html|title=The Element Promethium|last=Gagnon|first=Steve|work=Jefferson Lab|publisher=Science Education|access-date=26 February 2012}}</ref>

==Production==

The production methods for different isotopes vary, and only those for promethium-147 are given because it is the only isotope with industrial applications. Promethium-147 is produced in large quantities (compared to other isotopes) by bombarding uranium-235 with thermal neutrons. The output is relatively high, at 2.6% of the total product.{{sfn|Lavrukhina|Pozdnyakov|1966|p=115}} Another way to produce promethium-147 is via neodymium-147, which decays to promethium-147 with a short half-life. Neodymium-147 can be obtained either by bombarding enriched neodymium-146 with [[thermal neutron]]s<ref name="Russia" /> or by bombarding a [[uranium carbide]] target with energetic protons in a particle accelerator.<ref>{{cite book|title = Applications of inorganic mass spectrometry|year = 2011|page = 144|publisher = Springer|isbn = 978-3-642-21022-8|last1 = Hänninen|first1 = Pekka|last2 = Härmä|first2 = Harri}}</ref> Another method is to bombard uranium-238 with [[fast neutron]]s to cause [[fast fission]], which, among multiple reaction products, creates promethium-147.<ref name="De2001">{{cite book|title = Applications of inorganic mass spectrometry|isbn=978-0471345398
|year = 2001|author1=De Laeter |author2=J. R. |page = 205|publisher = Wiley-IEEE}}</ref><!--how is the promethium extracted chemically?-->

As early as the 1960s, Oak Ridge National Laboratory could produce 650&nbsp;grams of promethium per year{{sfn|Lavrukhina|Pozdnyakov|1966|p=116}} and was the world's only large-volume synthesis facility.<ref>{{cite book|title = On the Home Front: The Cold War Legacy of the Hanford Nuclear Site|year = 2007|edition = 3rd|publisher = University of Nebraska Press|page = 162|isbn = 978-0-8032-5995-9|last1 = Gerber|first1 = Michele Stenehjem|last2 = Findlay|first2 = John M.}}</ref> Gram-scale production of promethium has been discontinued in the U.S. in the early 1980s, but will possibly be resumed after 2010 at the [[High Flux Isotope Reactor]]. {{Update inline|date=December 2020}} In 2010, Russia was the only country producing promethium-147 on a relatively large scale.<ref name="Russia">{{cite book|title = Radioisotope Thin-Film Powered Microsystems|year = 2010|isbn = 978-1441967626|last1 = Duggirala|first1 = Rajesh|last2 = Lal|first2 = Amit|last3 = Radhakrishnan|first3 = Shankar|publisher = Springer|page=12|url=https://books.google.com/books?id=AoWbhNoLwnYC&pg=PA12}}</ref>

==Applications==
[[File:Pm,61.jpg|thumb|right|upright=0.9|[[Promethium(III) chloride]] being used as a light source for signals in a heat button]]
Only promethium-147 has uses outside laboratories.{{sfn|Emsley|2011|p=428}} It is obtained as the oxide or chloride,{{sfn|Lavrukhina|Pozdnyakov|1966|p=118}} in milligram quantities.{{sfn|Emsley|2011|p=428}} This isotope has a relatively long half-life, does not emit [[gamma rays]], and its radiation has a relatively small penetration depth in matter.{{sfn|Lavrukhina|Pozdnyakov|1966|p=118}}

Some signal lights use a [[luminous paint]] containing a [[phosphor]] that absorbs the beta radiation emitted by promethium-147 and emits light.<ref name="CRCel" />{{sfn|Emsley|2011|p=428}} This isotope does not cause aging of the phosphor, as alpha emitters do,{{sfn|Lavrukhina|Pozdnyakov|1966|p=118}} and therefore the light emission is stable for a few years.{{sfn|Lavrukhina|Pozdnyakov|1966|p=118}} Originally, [[radium]]-226 was used for the purpose, but it was later replaced by promethium-147 and [[tritium]] (hydrogen-3).<ref>{{Cite book|title = Man-made and natural radioactivity in environmental pollution and radiochronology|year = 2004|page = 78|isbn = 978-1-4020-1860-2|last1 = Tykva|first1 = Richard
|last2 = Berg|first2 = Dieter|publisher=Springer}}</ref> Promethium may be favored over tritium for [[nuclear safety]].<ref name="Deeter1993">{{cite book
|title = Disease and the Environment|year = 1993|author = Deeter, David P.|page = 187|publisher = Government Printing Office}}</ref>

In [[atomic battery|atomic batteries]], the beta particles emitted by promethium-147 are converted into electric current by sandwiching a small promethium source between two semiconductor plates. These batteries have a useful lifetime of about five years.<ref name="brit" /><ref name="CRCel" />{{sfn|Emsley|2011|p=428}} The first promethium-based battery was assembled in 1964 and generated "a few milliwatts of power from a volume of about 2 cubic inches, including shielding".<ref>{{cite journal|doi=10.1109/T-ED.1964.15271|title=Construction of a promethium-147 atomic battery|year=1964|last1=Flicker|first1=H.|last2=Loferski|first2=J. J.|last3=Elleman|first3=T. S.|journal=IEEE Transactions on Electron Devices|volume=11|issue=1|pages=2|bibcode=1964ITED...11....2F}}</ref>

Promethium is also used to measure the thickness of materials by measuring the amount of radiation from a promethium source that passes through the sample.<ref name="CRCel" />{{sfn|Emsley|2011|p=429}}<ref>{{cite book |title=The Terrorist Effect – Weapons of Mass Disruption: The Danger of Nuclear Terrorism |last1=Jones |first1=James William |last2=Haygood |first2=John R. |year=2011 |publisher=iUniverse |isbn=978-1-4620-3932-6 |page=180 |url=https://books.google.com/books?id=YwE0W6LsxygC&pg=PA180|access-date=January 13, 2012}}</ref> It has possible future uses in portable X-ray sources, and as auxiliary heat or power sources for space probes and satellites<ref name="Stwertka2002">{{cite book|title = A guide to the elements|year = 2002|publisher = Oxford University Press|author = Stwertka, Albert|page = 154|isbn = 978-0-19-515026-1}}</ref> (although the alpha emitter [[plutonium-238]] has become standard for most space-exploration-related uses).<ref name="Radioisotope2009">{{cite book|title = Radioisotope power systems: an imperative for maintaining U.S. leadership in space exploration|year = 2009|author = Radioisotope Power Systems Committee, National Research Council U.S.|page = 8|isbn = 978-0-309-13857-4|publisher = National Academies Press}}</ref>

Promethium-147 is also used, albeit in very small quantities (less than 330nCi), in some [[Philips]] CFL (Compact Fluorescent Lamp) glow switches in the PLC 22W/28W 15mm CFL range.<ref>https://www.msdsdigital.com/system/files/PHILIPS-CFL-15MM.pdf MSDS for the Philips CFL lamps containing Pm-147.</ref>

==Precautions==
The element has no biological role. Promethium-147 can emit gamma rays,  which are dangerous for all lifeforms, during its [[beta decay]].<ref name="Simmons1964">{{cite journal|title = Reed Business Information|year = 1964|author = Simmons, Howard|journal = New Scientist|page = 292|volume = 22|issue = 389}}</ref> Interactions with tiny quantities of promethium-147 are not hazardous if certain precautions are observed.<ref name="Army1987">{{cite book|title=Operator, organizational, direct support, and general support maintenance manual: installation, operation, and checkout procedures for Joint-Services Interior Intrusion Detection System (J-SIIDS).|url=https://books.google.com/books?id=JfoXAAAAYAAJ&pg=PP5|year=1991|publisher=Headquarters, Departments of the Army, Navy, and Air Force|page=5}}</ref> In general, gloves, footwear covers, safety glasses, and an outer layer of easily removed protective clothing should be used.<ref name="Pmlist" />

It is not known what human organs are affected by interaction with promethium; a possible candidate is the [[bone tissue]]s.<ref name="Pmlist" /> Sealed promethium-147 is not dangerous. However, if the packaging is damaged, then promethium becomes dangerous to the environment and humans. If [[radioactive contamination]] is found, the contaminated area should be washed with water and soap, but, even though promethium mainly affects the skin, the skin should not be abraded. If a promethium leak is found, the area should be identified as hazardous and evacuated, and emergency services must be contacted. No dangers from promethium aside from the radioactivity are known.<ref name="Pmlist">{{cite web |title=Radioactive Material Safety Data Sheet |author1=Stuart Hunt |author2=Associates Lt. |name-list-style=amp |url=https://www.stuarthunt.com/uploads/downloads/RMSDS%20Documents/Promethium-147-Sealed.pdf |access-date=2012-02-10 |archive-date=2021-09-15 |archive-url=https://web.archive.org/web/20210915131347/https://www.stuarthunt.com/uploads/downloads/RMSDS%20Documents/Promethium-147-Sealed.pdf |url-status=dead }}</ref>

==Notes==
{{Notelist}}

==References==
{{Reflist|30em}}

==Bibliography==
*{{cite book |last=Emsley |first=John |title=Nature's Building Blocks: An A-Z Guide to the Elements |url=https://books.google.com/books?id=2EfYXzwPo3UC&pg=PA428 |year=2011 |publisher=Oxford University Press |isbn=978-0-19-960563-7 |pages=428–430 }}
*{{cite book |title=Аналитическая химия технеция, прометия, астатина и франция (Analytical Chemistry of Technetium, Promethium, Astatine, and Francium) |language=ru |first1=Avgusta Konstantinovna |last1=Lavrukhina |first2=Aleksandr Aleksandrovich |last2=Pozdnyakov |year=1966 |publisher=[[Nauka (publisher)|Nauka]] }}
*2013, E.R. Scerri,''A tale of seven elements,'' Oxford University Press, Oxford, {{ISBN|9780195391312}}

==External links==
{{Commons|Promethium}}
{{Wiktionary|promethium}}
*[http://education.jlab.org/itselemental/ele061.html It's Elemental – Promethium]

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[[Category:Promethium| ]]
[[Category:Chemical elements]]
[[Category:Chemical elements with double hexagonal close-packed structure]]
[[Category:Lanthanides]]
[[Category:Prometheus]]
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