View source for Actinium

{{Distinguish|Actin|Actium}}
{{Use dmy dates|date=March 2014}}
{{Infobox actinium}}
'''Actinium''' is a [[chemical element]]; it has [[chemical symbol|symbol]] '''Ac''' and [[atomic number]]&nbsp;89. It was first isolated by [[Friedrich Oskar Giesel]] in 1902, who gave it the name ''emanium''; the element got its name by being wrongly identified with a substance [[André-Louis Debierne]] found in 1899 and called actinium. The [[actinide]] series, a set of 15 elements between actinium and [[lawrencium]] in the [[periodic table]], are named for actinium. Together with [[polonium]], [[radium]], and [[radon]], actinium was one of the first [[Primordial element|non-primordial radioactive element]]s to be isolated.

A soft, silvery-white [[radioactive]] metal, actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that prevents further oxidation. As with most [[lanthanide]]s and many [[actinide]]s, actinium assumes [[oxidation state]] +3 in nearly all its chemical compounds. Actinium is found only in traces in [[uranium]] and [[thorium]] ores as the [[isotope]] <sup>227</sup>Ac, which decays with a [[half-life]] of 21.772 years, predominantly emitting [[beta particle|beta]] and sometimes [[alpha particle]]s, and <sup>228</sup>Ac, which is beta active with a half-life of 6.15 hours. One [[tonne]] of natural [[uranium]] in ore contains about 0.2 milligrams of actinium-227, and one tonne of [[thorium]] contains about 5 nanograms of actinium-228. The close similarity of physical and chemical properties of actinium and [[lanthanum]] makes separation of actinium from the ore impractical. Instead, the element is prepared, in milligram amounts, by the neutron irradiation of {{chem2|^{226}Ra|link=radium}} in a [[nuclear reactor]]. Owing to its scarcity, high price and radioactivity, actinium has no significant industrial use. Its current applications include a neutron source and an agent for [[radiation therapy]].

==History==
[[André-Louis Debierne]], a French chemist, announced the discovery of a new element in 1899. He separated it from [[uraninite|pitchblende]] residues left by [[Marie Curie|Marie]] and [[Pierre Curie]] after they had extracted [[radium]].<ref name="Adloff"/> In 1899, Debierne described the substance as similar to [[titanium]]<ref>{{cite journal |title = Sur un nouvelle matière radio-active |first = André-Louis |last = Debierne |journal = Comptes Rendus |volume = 129 |pages = 593–595 |date = 1899 |url=http://gallica.bnf.fr/ark:/12148/bpt6k3085b/f593.table |language=fr}}</ref> and (in 1900) as similar to [[thorium]].<ref>{{cite journal |title = Sur un nouvelle matière radio-actif – l'actinium |first = André-Louis |last = Debierne |journal = Comptes Rendus |volume = 130 |pages = 906–908 |date = 1900–1901 |url=http://gallica.bnf.fr/ark:/12148/bpt6k3086n/f906.table |language=fr}}</ref> [[Friedrich Oskar Giesel]] found in 1902<ref>{{cite journal |title = Ueber Radium und radioactive Stoffe |first = Friedrich Oskar |last = Giesel |journal = Berichte der Deutschen Chemischen Gesellschaft |volume = 35 |issue = 3 |pages = 3608–3611 |date = 1902 |doi = 10.1002/cber.190203503187 |language=de|url=https://zenodo.org/record/1426058 }}</ref> a substance similar to [[lanthanum]] and called it "emanium" in 1904.<ref>{{cite journal |title = Ueber den Emanationskörper (Emanium) |first = Friedrich Oskar |last = Giesel |journal = Berichte der Deutschen Chemischen Gesellschaft |volume = 37 |issue = 2 |pages = 1696–1699 |date = 1904 |doi = 10.1002/cber.19040370280 |language=de|url=https://zenodo.org/record/1426108 }}</ref> After a comparison of the substances' half-lives determined by Debierne,<ref>{{cite journal |title = Sur l'actinium |first = André-Louis |last = Debierne |journal = Comptes Rendus |volume = 139 |pages = 538–540 |date = 1904 |language=fr}}</ref> [[Harriet Brooks]] in 1904, and [[Otto Hahn]] and [[Otto Sackur]] in 1905, Debierne's chosen name for the new element was retained because it had seniority, despite the contradicting chemical properties he claimed for the element at different times.<ref>{{cite journal |title = Ueber Emanium |first = Friedrich Oskar |last = Giesel |journal = Berichte der Deutschen Chemischen Gesellschaft |volume = 37 |issue = 2 |pages = 1696–1699 |date = 1904 |doi = 10.1002/cber.19040370280 |language=de|url=https://zenodo.org/record/1426108 }}</ref><ref>{{cite journal |title = Ueber Emanium |first = Friedrich Oskar |last = Giesel |journal = Berichte der Deutschen Chemischen Gesellschaft |volume = 38 |issue = 1 |pages = 775–778 |date = 1905 |doi = 10.1002/cber.190503801130 |url=https://zenodo.org/record/1426124 |language=de}}</ref>

Articles published in the 1970s<ref name="discovery">{{cite journal |title = The Discovery of Actinium |first = Harold W. |last = Kirby |journal = Isis |volume = 62 |issue = 3 |pages = 290–308
|date = 1971 |jstor=229943 |doi =10.1086/350760|s2cid = 144651011 }}</ref> and later<ref name="Adloff">{{cite journal |title = The centenary of a controversial discovery: actinium |first = J. P. |last = Adloff |journal = Radiochim. Acta |volume = 88 |pages = 123–128 |date = 2000 |doi = 10.1524/ract.2000.88.3-4.123 |issue = 3–4_2000|s2cid = 94016074 }}</ref> suggest that Debierne's results published in 1904 conflict with those reported in 1899 and 1900. Furthermore, the now-known chemistry of actinium precludes its presence as anything other than a minor constituent of Debierne's 1899 and 1900 results; in fact, the chemical properties he reported make it likely that he had, instead, accidentally identified [[protactinium]], which would not be discovered for another fourteen years, only to have it disappear due to its hydrolysis and adsorption onto his [[laboratory equipment]]. This has led some authors to advocate that Giesel alone should be credited with the discovery.<ref name="Kirby" /> A less confrontational vision of scientific discovery is proposed by Adloff.<ref name="Adloff" /> He suggests that hindsight criticism of the early publications should be mitigated by the then nascent state of radiochemistry: highlighting the prudence of Debierne's claims in the original papers, he notes that nobody can contend that Debierne's substance did not contain actinium.<ref name="Adloff" /> Debierne, who is now considered by the vast majority of historians as the discoverer, lost interest in the element and left the topic. Giesel, on the other hand, can rightfully be credited with the first preparation of radiochemically pure actinium and with the identification of its atomic number 89.<ref name="discovery" />

The name actinium originates from the [[Ancient Greek]] ''aktis, aktinos'' (ακτίς, ακτίνος), meaning beam or ray.<ref name="CRC" /> Its symbol Ac is also used in abbreviations of other compounds that have nothing to do with actinium, such as [[acetyl]], [[acetate]]<ref>{{cite book |author1=Gilley, Cynthia Brooke |author2=University of California, San Diego. Chemistry |title=New convertible isocyanides for the Ugi reaction; application to the stereoselective synthesis of omuralide |url=https://books.google.com/books?id=vJQPInUTy3QC&pg=PR11 |date=2008 |isbn=978-0-549-79554-4 |page=11}}</ref> and sometimes [[acetaldehyde]].<ref>{{cite book |author=Reimers, Jeffrey R. |title=Computational Methods for Large Systems: Electronic Structure Approaches for Biotechnology and Nanotechnology |url=https://books.google.com/books?id=Ca9z4_cH-W8C&pg=PA575 |date= 2011 |publisher=John Wiley and Sons |isbn=978-0-470-48788-4 |page=575}}</ref>

==Properties==
Actinium is a soft, silvery-white,<ref name="blueglow" /><ref name="brit">''Actinium'', in Encyclopædia Britannica, 15th edition, 1995, p. 70</ref> [[radioactive]], metallic element. Its estimated [[shear modulus]] is similar to that of [[lead]].<ref>Seitz, Frederick and Turnbull, David (1964) [https://books.google.com/books?id=F9V3a-0V3r8C&pg=PA289 ''Solid state physics: advances in research and applications'']. Academic Press. {{ISBN|0-12-607716-9}} pp. 289–291</ref> Owing to its strong radioactivity, actinium glows in the dark with a pale blue light, which originates from the surrounding air ionized by the emitted energetic particles.<ref>{{cite book |author=Richard A. Muller |title=Physics and Technology for Future Presidents: An Introduction to the Essential Physics Every World Leader Needs to Know |url=https://books.google.com/books?id=jMWCDsJesbcC&pg=PA136 |date= 2010 |publisher=Princeton University Press |isbn=978-0-691-13504-5 |pages=136–}}</ref> Actinium has similar chemical properties to [[lanthanum]] and other lanthanides, and therefore these elements are difficult to separate when extracting from uranium ores. [[Solvent extraction]] and [[ion chromatography]] are commonly used for the separation.<ref>{{cite journal |title = Chemistry of the Actinide Elements |volume = 1 |pages = 245–262 |date = 1952 |first1 = J. J. |last1 = Katz |doi = 10.1146/annurev.ns.01.120152.001333 |journal = [[Annual Review of Nuclear Science]] |last2 = Manning |first2 = W. M. |bibcode = 1952ARNPS...1..245K }}</ref>

The first element of the [[actinide]]s, actinium gave the set its name, much as [[lanthanum]] had done for the [[lanthanide]]s. The actinides are much more diverse than the lanthanides<ref name="Jorgensen">{{cite journal |last1=Jørgensen |first1=Christian |date=1973 |title=The Loose Connection between Electron Configuration and the Chemical Behavior of the Heavy Elements (Transuranics) |journal=Angewandte Chemie International Edition |volume=12 |issue=1 |pages=12–19 |doi=10.1002/anie.197300121}}</ref> and therefore it was not until 1945 that the most significant change to [[Dmitri Mendeleev]]'s [[periodic table]] since the recognition of the lanthanides, the [[actinide concept|introduction of the actinides]], was generally accepted after [[Glenn T. Seaborg]]'s research on the [[transuranium element]]s<ref>{{cite journal |title = The Transuranium Elements |first = Glenn T. |last = Seaborg |journal = Science |volume = 104 |issue = 2704 |date = 1946 |pages = 379–386 |jstor=1675046 |doi = 10.1126/science.104.2704.379 |pmid = 17842184 |bibcode = 1946Sci...104..379S }}</ref> (although it had been proposed as early as 1892 by British chemist Henry Bassett).<ref name="Thyssen">{{Cite book |last1=Thyssen |first1=P. |title=Handbook on the Physics and Chemistry of Rare Earths |last2=Binnemans |first2=K. |date=2011 |publisher=Elsevier |isbn=978-0-444-53590-0 |editor-last=Gschneidner |editor-first=K. A. Jr. |volume=41 |location=Amsterdam |pages=1–94 |chapter=Accommodation of the Rare Earths in the Periodic Table: A Historical Analysis |doi=10.1016/B978-0-444-53590-0.00001-7 |editor-last2=Bünzli |editor-first2=J-C.G |editor-last3=Vecharsky |editor-first3=Bünzli}}</ref>

Actinium reacts rapidly with oxygen and moisture in air forming a white coating of [[actinium oxide]] that impedes further oxidation.<ref name="blueglow">{{cite journal |title = Preparation of Actinium Metal |first1 = Joseph G. |last1 = Stites |journal = J. Am. Chem. Soc. |date = 1955 |volume = 77 |issue = 1 |pages = 237–240 |doi = 10.1021/ja01606a085 |last2 = Salutsky |first2 = Murrell L. |last3 = Stone |first3 = Bob D.|bibcode = 1955JAChS..77..237S }}</ref> As with most lanthanides and actinides, actinium exists in the [[oxidation state]] +3, and the Ac<sup>3+</sup> ions are colorless in solutions.<ref name="bse" /> The oxidation state +3 originates from the [Rn] 6d<sup>1</sup>7s<sup>2</sup> electronic configuration of actinium, with three valence electrons that are easily donated to give the stable closed-shell structure of the [[noble gas]] [[radon]].<ref name="brit" /> Although the 5f orbitals are unoccupied in an actinium atom, it can be used as a valence orbital in actinium complexes and hence it is generally considered the first 5f element by authors working on it.<ref>{{cite journal |last1=Tomeček |first1=Josef |last2=Li |first2=Cen |first3=Georg |last3=Schreckenbach |date=2023 |title=Actinium coordination chemistry: A density functional theory study with monodentate and bidentate ligands |url= |journal=Journal of Computational Chemistry |volume=44 |issue=3 |pages=334–345 |doi=10.1002/jcc.26929 |pmid=35668552 |s2cid=249433367 |access-date=}}</ref><ref>{{cite journal |last1=Deblonde |first1=Gauthier J.-P. |last2=Zavarin |first2=Mavrik |first3=Annie B. |last3=Kersting |date=2021 |title=The coordination properties and ionic radius of actinium: A 120-year-old enigma |url= |journal=Coordination Chemistry Reviews |volume=446 |issue= |page=214130 |doi=10.1016/j.ccr.2021.214130 |access-date=|doi-access=free }}</ref><ref name="AcNatureChem"/> Ac<sup>3+</sup> is the largest of all known tripositive ions and its first coordination sphere contains approximately 10.9 ± 0.5 water molecules.<ref>{{cite journal |last1=Ferrier |first1=Maryline G. |last2=Stein |first2=Benjamin W. |first3=Enrique R. |last3=Batista |first4=John M. |last4=Berg |first5=Eva R. |last5=Birnbaum |first6=Jonathan W. |last6=Engle |first7=Kevin D. |last7=John |first8=Stosh A. |last8=Kozimor |first9=Juan S. |last9=Lezama Pacheco |first10=Lindsay N. |last10=Redman |date=2017 |title=Synthesis and Characterization of the Actinium Aquo Ion |journal=ACS Central Science |volume=3 |issue=3 |pages=176–185 |doi=10.1021/acscentsci.6b00356|pmid=28386595 |pmc=5364452 }}</ref>

==Chemical compounds==
{{Main|Actinium compounds}}
Due to actinium's intense radioactivity, only a limited number of actinium compounds are known. These include: [[Actinium fluoride|AcF<sub>3</sub>]], [[Actinium(III) chloride|AcCl<sub>3</sub>]], [[Actinium(III) bromide|AcBr<sub>3</sub>]], [[Actinium oxyfluoride|AcOF]], [[Actinium(III) oxychloride|AcOCl]], [[Actinium(III) oxybromide|AcOBr]], [[Actinium(III) sulfide|Ac<sub>2</sub>S<sub>3</sub>]], [[Actinium oxide|Ac<sub>2</sub>O<sub>3</sub>]], [[Actinium(III) phosphate|AcPO<sub>4</sub>]] and [[Actinium(III) nitrate|Ac(NO<sub>3</sub>)<sub>3</sub>]]. They all contain actinium in the oxidation state +3.<ref name="bse" /><ref name="j2" /> In particular, the lattice constants of the analogous lanthanum and actinium compounds differ by only a few percent.<ref name="j2" />

{| Class = "wikitable collapsible collapsed" style = "text-align: center"
! Formula
! color
! symmetry
! [[space group]]
! No
! [[Pearson symbol]]
! ''a'' (pm)
! ''b'' (pm)
! ''c'' (pm)
! ''Z''
! density, <br />g/cm<sup>3</sup>
|-
| Ac
| silvery
| ''[[Cubic crystal system|fcc]]''<ref name="ach">{{cite journal |doi=10.1016/0022-1902(61)80369-2 |last1=Farr |date=1961 |first1=J. |pages=42–47 |volume=18 |journal=Journal of Inorganic and Nuclear Chemistry |title=The crystal structure of actinium metal and actinium hydride |last2=Giorgi |first2=A. L. |last3=Bowman |first3=M. G. |last4=Money |first4=R. K.|osti=4397640 }}</ref>
| Fm{{overline|3}}m
| 225
| cF4
| 531.1
| 531.1
| 531.1
| 4
| 10.07
|-
| AcH<sub>2</sub>
|unknown
| cubic<ref name="ach" />
| Fm{{overline|3}}m
| 225
| cF12
| 567
| 567
| 567
| 4
| 8.35
|-
| Ac<sub>2</sub>O<sub>3</sub>
| white<ref name="blueglow" />
| [[Trigonal crystal system|trigonal]]<ref name="aco">{{cite journal |doi=10.1107/S0365110X49001016 |last1=Zachariasen |date=1949 |first1=W. H. |pages=388–390 |volume=2 |journal=Acta Crystallographica |title=Crystal chemical studies of the 5f-series of elements. XII. New compounds representing known structure types |issue=6|doi-access=free |bibcode=1949AcCry...2..388Z }}</ref>
| P{{overline|3}}m1
| 164
| hP5
| 408
| 408
| 630
| 1
| 9.18
|-
| Ac<sub>2</sub>S<sub>3</sub>
| black
| cubic<ref name="acs">{{cite journal |doi=10.1107/S0365110X49000126 |last1=Zachariasen |date=1949 |first1=W. H. |pages=57–60 |volume=2 |journal=Acta Crystallographica |title=Crystal chemical studies of the 5f-series of elements. VI. The Ce2S3-Ce3S4 type of structure|issue=1 |bibcode=1949AcCry...2...57Z |url=http://journals.iucr.org/q/issues/1949/01/00/a00105/a00105.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://journals.iucr.org/q/issues/1949/01/00/a00105/a00105.pdf |archive-date=2022-10-09 |url-status=live }}</ref>
| I{{overline|4}}3d
| 220
| cI28
| 778.56
| 778.56
| 778.56
| 4
| 6.71
|-
| AcF<sub>3</sub>
| white<ref name="m71">Meyer, p. 71</ref>
| [[Hexagonal crystal system|hexagonal]]<ref name="j2" /><ref name="aco" />
| P{{overline|3}}c1
| 165
| hP24
| 741
| 741
| 755
| 6
| 7.88
|-
| AcCl<sub>3</sub>
|white
| hexagonal<ref name="j2" /><ref name="accl">{{cite journal |doi=10.1107/S0365110X48000703 |last1=Zachariasen |date=1948 |first1=W. H. |pages=265–268 |volume=1 |journal=Acta Crystallographica |title=Crystal chemical studies of the 5f-series of elements. I. New structure types |issue=5|doi-access=free |bibcode=1948AcCry...1..265Z }}</ref>
| P6<sub>3</sub>/m
| 165
| hP8
| 764
| 764
| 456
| 2
| 4.8
|-
| AcBr<sub>3</sub>
| white<ref name="j2" />
| hexagonal<ref name="accl" />
| P6<sub>3</sub>/m
| 165
| hP8
| 764
| 764
| 456
| 2
| 5.85
|-
| AcOF
| white<ref name="m87" />
| cubic<ref name="j2" />
| Fm{{overline|3}}m
|
|
| 593.1
|
|
|
| 8.28
|-
| AcOCl
|white
| [[Tetragonal crystal system|tetragonal]]<ref name="j2" />
|
|
|
| 424
| 424
| 707
|
| 7.23
|-
| AcOBr
|white
| tetragonal<ref name="j2" />
|
|
|
| 427
| 427
| 740
|
| 7.89
|-
| AcPO<sub>4</sub>·0.5H<sub>2</sub>O
|unknown
| hexagonal<ref name="j2" />
|
|
|
| 721
| 721
| 664
|
| 5.48
|}

Here ''a'', ''b'' and ''c'' are lattice constants, No is space group number and ''Z'' is the number of [[formula unit]]s per [[unit cell]]. Density was not measured directly but calculated from the lattice parameters.

===Oxides===
{{Main|Actinium(III) oxide}}
[[Actinium oxide]] (Ac<sub>2</sub>O<sub>3</sub>) can be obtained by heating the hydroxide at {{cvt|500|°C}} or the [[oxalate]] at {{cvt|1100|°C}}, in vacuum. Its crystal lattice is [[Isomorphism (crystallography)|isotypic]] with the oxides of most trivalent rare-earth metals.<ref name="j2" />

===Halides===
[[Actinium trifluoride]] can be produced either in solution or in solid reaction. The former reaction is carried out at room temperature, by adding [[hydrofluoric acid]] to a solution containing actinium ions. In the latter method, actinium metal is treated with hydrogen fluoride vapors at {{cvt|700|°C}} in an all-platinum setup. Treating actinium trifluoride with [[ammonium hydroxide]] at {{cvt|900|–|1000|°C}} yields [[oxyfluoride]] AcOF. Whereas lanthanum oxyfluoride can be easily obtained by burning lanthanum trifluoride in air at {{cvt|800|°C}} for an hour, similar treatment of actinium trifluoride yields no AcOF and only results in melting of the initial product.<ref name="j2" /><ref name="m87">Meyer, pp. 87–88</ref>

:AcF<sub>3</sub> + 2 NH<sub>3</sub> + H<sub>2</sub>O → AcOF + 2 NH<sub>4</sub>F

Actinium trichloride is obtained by reacting actinium hydroxide or [[oxalate]] with [[carbon tetrachloride]] vapors at temperatures above {{cvt|960|°C}}. Similarly to the oxyfluoride, actinium [[oxychloride]] can be prepared by hydrolyzing actinium trichloride with [[ammonium hydroxide]] at {{cvt|1000|°C}}. However, in contrast to the oxyfluoride, the oxychloride could well be synthesized by igniting a solution of actinium trichloride in [[hydrochloric acid]] with [[ammonia]].<ref name="j2" />

Reaction of [[aluminium bromide]] and actinium oxide yields [[Actinium(III) bromide|actinium tribromide]]:
:Ac<sub>2</sub>O<sub>3</sub> + 2 AlBr<sub>3</sub> → 2 AcBr<sub>3</sub> + Al<sub>2</sub>O<sub>3</sub>

and treating it with ammonium hydroxide at {{cvt|500|°C}} results in the oxybromide AcOBr.<ref name="j2" />

===Other compounds===
[[Actinium hydride]] was obtained by reduction of actinium trichloride with potassium at {{cvt|300|°C}}, and its structure was deduced by analogy with the corresponding LaH<sub>2</sub> hydride. The source of hydrogen in the reaction was uncertain.<ref>Meyer, p. 43</ref>

Mixing [[monosodium phosphate]] (NaH<sub>2</sub>PO<sub>4</sub>) with a solution of actinium in hydrochloric acid yields white-colored actinium phosphate hemihydrate (AcPO<sub>4</sub>·0.5H<sub>2</sub>O), and heating [[actinium oxalate]] with [[hydrogen sulfide]] vapors at {{cvt|1400|°C}} for a few minutes results in a black [[actinium sulfide]] Ac<sub>2</sub>S<sub>3</sub>. It may possibly be produced by acting with a mixture of [[hydrogen sulfide]] and [[carbon disulfide]] on [[actinium oxide]] at {{cvt|1000|°C}}.<ref name="j2">{{cite journal |doi=10.1021/ja01158a034 |last1=Fried |date=1950 |first1=Sherman |pages=771–775 |volume=72 |journal=Journal of the American Chemical Society |last2=Hagemann |first2=French |last3=Zachariasen |first3=W. H. |title=The Preparation and Identification of Some Pure Actinium Compounds |issue=2|bibcode=1950JAChS..72..771F }}</ref>

==Isotopes==
{{Main|Isotopes of actinium}}
Naturally occurring actinium is principally composed of two radioactive [[isotope]]s; {{chem|227|Ac}} (from the radioactive family of {{chem|235|U}}) and {{chem|228|Ac}} (a granddaughter of {{chem|232|Th}}). {{chem|227|Ac}} decays mainly as a [[beta decay|beta emitter]] with a very small energy, but in 1.38% of cases it emits an [[alpha particle]], so it can readily be identified through [[alpha spectrometry]].<ref name="Kirby" /> Thirty-three [[radioisotope]]s have been identified, the most stable being {{chem|227|Ac}} with a [[half-life]] of 21.772 years, [[actinium-225|{{chem|225|Ac}}]] with a half-life of 10.0 days and {{chem|226|Ac}} with a half-life of 29.37 hours. All remaining [[radioactive decay|radioactive]] isotopes have half-lives that are less than 10 hours and the majority of them have half-lives shorter than one minute. The shortest-lived known isotope of actinium is {{chem|217|Ac}} (half-life of 69 nanoseconds) which decays through [[alpha decay]]. Actinium also has two known [[meta state]]s.{{NUBASE2016|ref}} The most significant isotopes for chemistry are <sup>225</sup>Ac, <sup>227</sup>Ac, and <sup>228</sup>Ac.<ref name="Kirby" />

Purified {{chem|227|Ac}} comes into equilibrium with its decay products after about a half of year. It decays according to its 21.772-year half-life emitting mostly beta (98.62%) and some alpha particles (1.38%);{{NUBASE2016|ref}} the successive decay products are part of the [[actinium series]]. Owing to the low available amounts, low energy of its beta particles (maximum 44.8&nbsp;keV) and low intensity of alpha radiation, {{chem|227|Ac}} is difficult to detect directly by its emission and it is therefore traced via its decay products.<ref name="bse">[http://bse.sci-lib.com/article008169.html Actinium], [[Great Soviet Encyclopedia]] (in Russian)</ref> The isotopes of actinium range in [[atomic weight]] from 203&nbsp;[[atomic mass unit|u]] ({{chem|203|Ac}}) to 236&nbsp;u ({{chem|236|Ac}}).{{NUBASE2016|ref}}

{| class="wikitable" style="text-align:center"
 !Isotope
 !Production
 !Decay
 !Half-life
 |-
 |<sup>221</sup>Ac
 |align=right |<sup>232</sup>Th(d,9n)→<sup>225</sup>Pa(α)→<sup>221</sup>Ac
 |α
 |52 ms
 |-
 |<sup>222</sup>Ac
 |align=right |<sup>232</sup>Th(d,8n)→<sup>226</sup>Pa(α)→<sup>222</sup>Ac
 |α
 |5.0 s
 |-
 |<sup>223</sup>Ac
 |align=right |<sup>232</sup>Th(d,7n)→<sup>227</sup>Pa(α)→<sup>223</sup>Ac
 |α
 |2.1 min
 |-
 |<sup>224</sup>Ac
 |align=right |<sup>232</sup>Th(d,6n)→<sup>228</sup>Pa(α)→<sup>224</sup>Ac
 |α
 |2.78 hours
 |-
 |<sup>225</sup>Ac
 |align=right |<sup>232</sup>Th(n,γ)→<sup>233</sup>Th(β<sup>−</sup>)→<sup>233</sup>Pa(β<sup>−</sup>)→<sup>233</sup>U(α)→<sup>229</sup>Th(α)→<sup>225</sup>Ra(β<sup>−</sup>)→<sup>225</sup>Ac
 |α
 |10 days
 |-
 |<sup>226</sup>Ac
 |align=right |<sup>226</sup>Ra(d,2n)→<sup>226</sup>Ac
 |α, β<sup>−</sup> <br />electron capture
 |29.37 hours
 |-
 |<sup>227</sup>Ac
 |align=right |<sup>235</sup>U(α)→<sup>231</sup>Th(β<sup>−</sup>)→<sup>231</sup>Pa(α)→<sup>227</sup>Ac
 |α, β<sup>−</sup>
 |21.77 years
 |-
 |<sup>228</sup>Ac
 |align=right |<sup>232</sup>Th(α)→<sup>228</sup>Ra(β<sup>−</sup>)→<sup>228</sup>Ac
 |β<sup>−</sup>
 |6.15 hours
 |-
 |<sup>229</sup>Ac
 |align=right |<sup>228</sup>Ra(n,γ)→<sup>229</sup>Ra(β<sup>−</sup>)→<sup>229</sup>Ac
 |β<sup>−</sup>
 |62.7 min
 |-
 |<sup>230</sup>Ac
 |align=right |<sup>232</sup>Th(d,α)→<sup>230</sup>Ac
 |β<sup>−</sup>
 |122 s
 |-
 |<sup>231</sup>Ac
 |align=right |<sup>232</sup>Th(γ,p)→<sup>231</sup>Ac
 |β<sup>−</sup>
 |7.5 min
 |-
 |<sup>232</sup>Ac
 |align=right |<sup>232</sup>Th(n,p)→<sup>232</sup>Ac
 |β<sup>−</sup>
 |119 s
 |}

==Occurrence and synthesis==
[[File:Uraninite-39029.jpg|upright=0.70|thumb|[[Uraninite]] ores have elevated concentrations of actinium.]]
Actinium is found only in traces in [[uranium]] ores&nbsp;– one tonne of uranium in ore contains about 0.2 milligrams of <sup>227</sup>Ac<ref name="Hagemann1950">{{cite journal |doi=10.1021/ja01158a033 |last1=Hagemann |date=1950 |first1=French |pages=768–771 |volume=72 |journal=Journal of the American Chemical Society |title=The Isolation of Actinium |issue=2|bibcode=1950JAChS..72..768H }}</ref><ref name="g946">{{Greenwood&Earnshaw2nd|page=946}}</ref> – and in [[thorium]] ores, which contain about 5 nanograms of <sup>228</sup>Ac per one tonne of thorium. The actinium [[isotope]] <sup>227</sup>Ac is a transient member of the [[Decay chain#Actinium series|uranium-actinium series]] [[decay chain]], which begins with the parent isotope [[Uranium-235|<sup>235</sup>U]] (or [[Plutonium-239|<sup>239</sup>Pu]]) and ends with the stable lead isotope [[lead-207|<sup>207</sup>Pb]]. The isotope <sup>228</sup>Ac is a transient member of the [[thorium series]] decay chain, which begins with the parent isotope [[Thorium-232|<sup>232</sup>Th]] and ends with the stable lead isotope [[lead-208|<sup>208</sup>Pb]]. Another actinium isotope (<sup>225</sup>Ac) is transiently present in the [[neptunium series]] [[decay chain]], beginning with [[Neptunium-237|<sup>237</sup>Np]] (or [[Uranium-233|<sup>233</sup>U]]) and ending with thallium ([[thallium-205|<sup>205</sup>Tl]]) and near-stable bismuth ([[bismuth-209|<sup>209</sup>Bi]]); even though all [[primordial nuclide|primordial]] <sup>237</sup>Np has decayed away, it is continuously produced by neutron knock-out reactions on natural <sup>238</sup>U.

The low natural concentration, and the close similarity of physical and chemical properties to those of lanthanum and other lanthanides, which are always abundant in actinium-bearing ores, render separation of actinium from the ore impractical. The most concentrated actinium sample prepared from raw material consisted of 7 micrograms of <sup>227</sup>Ac in less than 0.1 milligrams of La<sub>2</sub>O<sub>3</sub>, and complete separation was never achieved.<ref name=KirbyReview>{{Cite book |last1=Kirby |first1=H. W. |url=http://link.springer.com/10.1007/978-94-007-0211-0_2 |title=Actinium |last2=Morss |first2=Lester R. |date=2010 |publisher=Springer Netherlands |isbn=978-94-007-0210-3 |editor-last=Morss |editor-first=Lester R. |location=Dordrecht |pages=18–51 |language=en |doi=10.1007/978-94-007-0211-0_2 |editor-last2=Edelstein |editor-first2=Norman M. |editor-last3=Fuger |editor-first3=Jean}}</ref> Instead, actinium is prepared, in milligram amounts, by the neutron irradiation of {{chem2|^{226}Ra|link=Radium-226}} in a [[nuclear reactor]].<ref name="g946" /><ref>{{cite book |author=Emeleus, H. J. |title=Advances in inorganic chemistry and radiochemistry |url=https://books.google.com/books?id=K5_LSQqeZ_IC&pg=PA16 |date= 1987 |publisher=Academic Press |isbn=978-0-12-023631-2 |pages=16–}}</ref>
:<chem>^{226}_{88}Ra + ^{1}_{0}n -> ^{227}_{88}Ra ->[\beta^-][42.2 \ \ce{min}] ^{227}_{89}Ac</chem>
The reaction yield is about 2% of the radium weight. <sup>227</sup>Ac can further capture neutrons resulting in small amounts of <sup>228</sup>Ac. After the synthesis, actinium is separated from radium and from the products of decay and nuclear fusion, such as thorium, polonium, lead and bismuth. The extraction can be performed with [[thenoyltrifluoroacetone]]-[[benzene]] solution from an aqueous solution of the radiation products, and the selectivity to a certain element is achieved by adjusting the [[pH]] (to about 6.0 for actinium).<ref name="Hagemann1950" /> An alternative procedure is anion exchange with an appropriate [[resin]] in [[nitric acid]], which can result in a separation factor of 1,000,000 for radium and actinium vs. thorium in a two-stage process. Actinium can then be separated from radium, with a ratio of about 100, using a low cross-linking cation exchange resin and nitric acid as [[eluant]].<ref name="sep" />

<sup>225</sup>Ac was first produced artificially at the [[Institute for Transuranium Elements]] (ITU) in Germany using a [[cyclotron]] and at [[St George Hospital (Sydney)|St George Hospital]] in Sydney using a [[Linear particle accelerator|linac]] in 2000.<ref>{{cite journal |doi = 10.1016/j.apradiso.2008.11.012 |date = 2009 |author = Melville, G |author2 = Allen, Bj |title = Cyclotron and linac production of Ac-225 |volume = 67 |issue = 4 |pages = 549–55 |pmid = 19135381 |journal = Applied Radiation and Isotopes|bibcode = 2009AppRI..67..549M }}</ref> This rare isotope has potential applications in radiation therapy and is most efficiently produced by bombarding a radium-226 target with 20–30&nbsp;MeV [[deuterium]] ions. This reaction also yields <sup>226</sup>Ac which however decays with a half-life of 29 hours and thus does not contaminate <sup>225</sup>Ac.<ref>{{cite book |last1=Russell |first1=Pamela J. |last2=Jackson |first2=Paul |last3=Kingsley |first3=Elizabeth Anne |year=2003 |url=https://books.google.com/books?id=K1y6k5bdlWkC&pg=PA336 |title=Prostate cancer methods and protocols |publisher=Humana Press |isbn=0-89603-978-1 |page=336}}{{Dead link|date=April 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

Actinium metal has been prepared by the reduction of actinium fluoride with [[lithium]] vapor in vacuum at a temperature between {{cvt|1100|and|1300|°C}}. Higher temperatures resulted in evaporation of the product and lower ones lead to an incomplete transformation. Lithium was chosen among other [[alkali metal]]s because its fluoride is most volatile.<ref name="CRC">Hammond, C. R. ''The Elements'' in {{RubberBible86th}}</ref><ref name="blueglow" />

==Applications==
Owing to its scarcity, high price and radioactivity, <sup>227</sup>Ac currently has no significant industrial use, but <sup>225</sup>Ac is currently being studied for use in cancer treatments such as targeted alpha therapies.<ref name="CRC" /><ref name="AcNatureChem">{{Cite journal|last1=Deblonde|first1=Gauthier J.-P.|last2=Abergel|first2=Rebecca J.|date=2016-10-21|title=Active actinium|journal=Nature Chemistry|language=en|volume=8|issue=11|pages=1084|doi=10.1038/nchem.2653|doi-access=free|pmid=27768109 |issn=1755-4349|bibcode=2016NatCh...8.1084D|osti=1458479|osti-access=free}}</ref><!--http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=4066566-->
<sup>227</sup>Ac is highly radioactive and was therefore studied for use as an active element of [[radioisotope thermoelectric generator]]s, for example in spacecraft. The oxide of <sup>227</sup>Ac pressed with [[beryllium]] is also an efficient [[neutron source]] with the activity exceeding that of the standard americium-beryllium and radium-beryllium pairs.<ref name="b1">Russell, Alan M. and Lee, Kok Loong (2005) [https://books.google.com/books?id=fIu58uZTE-gC&pg=PA470 ''Structure-property relations in nonferrous metals'']. Wiley. {{ISBN|0-471-64952-X}}, pp. 470–471</ref> In all those applications, <sup>227</sup>Ac (a beta source) is merely a progenitor which generates alpha-emitting isotopes upon its decay. Beryllium captures alpha particles and emits neutrons owing to its large cross-section for the (α,n) nuclear reaction:

: <chem>^{9}_{4}Be + ^{4}_{2}He -> ^{12}_{6}C + ^{1}_{0}n + \gamma</chem>

The <sup>227</sup>AcBe neutron sources can be applied in a [[neutron probe]]&nbsp;– a standard device for measuring the quantity of water present in soil, as well as moisture/density for quality control in highway construction.<ref>Majumdar, D. K. (2004) [https://books.google.com/books?id=hf1j9v4v3OEC&pg=PA108 ''Irrigation Water Management: Principles and Practice'']. {{ISBN|81-203-1729-7}} p. 108</ref><ref>Chandrasekharan, H. and Gupta, Navindu (2006) [https://books.google.com/books?id=45IDh4Lt8xsC&pg=PA203 ''Fundamentals of Nuclear Science – Application in Agriculture'']. {{ISBN|81-7211-200-9}} pp. 202 ff</ref> Such probes are also used in well logging applications, in [[neutron radiography]], tomography and other radiochemical investigations.<ref>{{cite journal |title = Neutron Spectrum of an Actinium–Beryllium Source |first1 = W. R. |last1 = Dixon |journal = Can. J. Phys. |volume = 35 |issue = 6 |pages = 699–702 |date = 1957 |doi = 10.1139/p57-075 |last2 = Bielesch |first2 = Alice |last3 = Geiger |first3 = K. W.|bibcode = 1957CaJPh..35..699D }}</ref>
[[File:DOTA polyaminocarboxylic acid.png|thumb|upright=0.70|Chemical structure of the [[DOTA (chelator)|DOTA]] carrier for <sup>225</sup>Ac in radiation therapy]]
<sup>225</sup>Ac is applied in medicine to produce {{chem2|^{213}Bi|link=Bismuth-213}} in a reusable generator<ref name="sep">{{cite journal |doi = 10.1016/j.apradiso.2004.12.003 |date = 2005 |volume = 62 |issue = 5 |pages =667–679 |title = Production of actinium-225 for alpha particle mediated radioimmunotherapy |last1 = Bolla |first1 = Rose A. |journal = Applied Radiation and Isotopes |pmid = 15763472 |last2 = Malkemus |first2 = D. |last3 = Mirzadeh |first3 = S.|bibcode = 2005AppRI..62..667B }}</ref> or can be used alone as an agent for [[radiation therapy]], in particular targeted alpha therapy (TAT). This isotope has a half-life of 10 days, making it much more suitable for radiation therapy than <sup>213</sup>Bi (half-life 46 minutes).<ref name="AcNatureChem" /> Additionally, <sup>225</sup>Ac decays to nontoxic <sup>209</sup>Bi rather than toxic [[lead]], which is the final product in the decay chains of several other candidate isotopes, namely <sup>227</sup>Th, <sup>228</sup>Th, and <sup>230</sup>U.<ref name="AcNatureChem" /> Not only <sup>225</sup>Ac itself, but also its daughters, emit alpha particles which kill cancer cells in the body. The major difficulty with application of <sup>225</sup>Ac was that intravenous injection of simple actinium complexes resulted in their accumulation in the bones and liver for a period of tens of years. As a result, after the cancer cells were quickly killed by alpha particles from <sup>225</sup>Ac, the radiation from the actinium and its daughters might induce new mutations. To solve this problem, <sup>225</sup>Ac was bound to a [[Chelation|chelating]] agent, such as [[citrate]], [[ethylenediaminetetraacetic acid]] (EDTA) or [[pentetic acid|diethylene triamine pentaacetic acid]] (DTPA). This reduced actinium accumulation in the bones, but the excretion from the body remained slow. Much better results were obtained with such chelating agents as HEHA ({{nowrap|1,4,7,10,13,16-hexaazacyclohexadecane-N,N′,N″,N‴,N‴′,N‴″-hexaacetic acid}})<ref>{{cite journal |title=Improved in Vivo Stability of Actinium-225 Macrocyclic Complexes|pmid=10425108|journal=J Med Chem |date=1999 |volume=42|issue=15|pages=2988–9|author=Deal K.A.|author2=Davis I.A.|author3=Mirzadeh S.|author4=Kennel S.J.|author5=Brechbiel M.W.|name-list-style=amp |doi=10.1021/jm990141f}}</ref> or [[DOTA (chelator)|DOTA]] ({{nowrap|1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid}}) coupled to [[trastuzumab]], a [[monoclonal antibody]] that interferes with the [[HER2/neu]] [[Receptor (biochemistry)|receptor]]. The latter delivery combination was tested on mice and proved to be effective against [[leukemia]], [[lymphoma]], [[breast cancer|breast]], [[Ovarian cancer|ovarian]], [[neuroblastoma]] and [[prostate cancer]]s.<ref>{{cite journal|last1=McDevitt|first1=Michael R.|last2=Ma|first2=Dangshe|last3=Lai|first3=Lawrence T.|last4=Simon|first4=Jim|last5=Borchardt|first5=Paul|last6=Frank|first6=R. Keith|last7=Wu|first7=Karen|last8=Pellegrini|first8=Virginia|last9=Curcio|first9=Michael J.|last10=Miederer|first10=Matthias|last11=Bander|first11=Neil H.|last12=Scheinberg|first12=David A.|display-authors=3|title=Tumor Therapy with Targeted Atomic Nanogenerators|date=2001|journal=Science|volume=294|issue=5546|pages=1537–1540|doi=10.1126/science.1064126|bibcode=2001Sci...294.1537M|pmid=11711678|s2cid=11782419|url=https://www.researchgate.net/publication/11642922}}</ref><ref>{{cite journal |url=http://cancerres.aacrjournals.org/content/63/16/5084.full.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://cancerres.aacrjournals.org/content/63/16/5084.full.pdf |archive-date=2022-10-09 |url-status=live |title=Targeted Actinium-225 in Vivo Generators for Therapy of Ovarian Cancer |author=Borchardt, Paul E. |journal=Cancer Research |volume=63 |issue=16 |pages= 5084–5090 |date=2003 |pmid=12941838|display-authors=etal}}</ref><ref>{{cite journal |author=Ballangrud, A. M. |title=Alpha-particle emitting atomic generator (Actinium-225)-labeled trastuzumab (herceptin) targeting of breast cancer spheroids: efficacy versus HER2/neu expression |journal=Clinical Cancer Research |volume=10 |issue=13 |pages=4489–97 |date=2004 |pmid=15240541 |doi=10.1158/1078-0432.CCR-03-0800|display-authors=etal|doi-access=free }}</ref>

The medium half-life of <sup>227</sup>Ac (21.77 years) makes it a very convenient radioactive isotope in modeling the slow vertical mixing of oceanic waters. The associated processes cannot be studied with the required accuracy by direct measurements of current velocities (of the order 50 meters per year). However, evaluation of the concentration depth-profiles for different isotopes allows estimating the mixing rates. The physics behind this method is as follows: oceanic waters contain homogeneously dispersed <sup>235</sup>U. Its decay product, <sup>231</sup>Pa, gradually precipitates to the bottom, so that its concentration first increases with depth and then stays nearly constant. <sup>231</sup>Pa decays to <sup>227</sup>Ac; however, the concentration of the latter isotope does not follow the <sup>231</sup>Pa depth profile, but instead increases toward the sea bottom. This occurs because of the mixing processes which raise some additional <sup>227</sup>Ac from the sea bottom. Thus analysis of both <sup>231</sup>Pa and <sup>227</sup>Ac depth profiles allows researchers to model the mixing behavior.<ref>{{cite journal |last1=Nozaki |first1=Yoshiyuki |title=Excess <sup>227</sup>Ac in deep ocean water |journal=Nature |volume=310 |pages=486–488 |date=1984 |doi=10.1038/310486a0 | issue=5977 | bibcode = 1984Natur.310..486N|s2cid=4344946 }}</ref><ref>{{cite journal |last1=Geibert |first1=W. |last2=Rutgers Van Der Loeff |first2=M. M. |last3=Hanfland |first3=C. |last4=Dauelsberg |first4=H.-J. |title=Actinium-227 as a deep-sea tracer: sources, distribution and applications |journal=Earth and Planetary Science Letters |volume=198 |issue=1–2 |pages=147–165 |date=2002 |doi=10.1016/S0012-821X(02)00512-5 |bibcode=2002E&PSL.198..147G|url=https://doi.pangaea.de/10.1594/PANGAEA.90616 }}</ref>

There are theoretical predictions that AcH<sub>x</sub> hydrides (in this case with very high pressure) are a candidate for a near [[room-temperature superconductor]] as they have T<sub>c</sub> significantly higher than H<sub>3</sub>S, possibly near 250&nbsp;K.<ref>{{Cite journal|last1=Semenok|first1=Dmitrii V.|last2=Kvashnin|first2=Alexander G.|last3=Kruglov|first3=Ivan A.|last4=Oganov|first4=Artem R.|date=2018-04-19|title=Actinium hydrides AcH<sub>10</sub>, AcH<sub>12</sub>, AcH<sub>16</sub> as high-temperature conventional superconductors|journal=The Journal of Physical Chemistry Letters|volume=9|issue=8|pages=1920–1926|doi=10.1021/acs.jpclett.8b00615|pmid=29589444|issn=1948-7185|arxiv=1802.05676|s2cid=4620593}}</ref>

==Precautions==
<sup>227</sup>Ac is highly radioactive and experiments with it are carried out in a specially designed laboratory equipped with a tight [[glove box]]. When actinium trichloride is administered intravenously to rats, about 33% of actinium is deposited into the bones and 50% into the liver. Its toxicity is comparable to, but slightly lower, than that of americium and plutonium.<ref>{{cite journal |doi = 10.2172/4406766 |title = Toxicology of Actinium Equilibrium Mixture |first2 = J. |last1 = Langham |last2 = Storer |first1 = W. |date = 1952 | journal = Los Alamos Scientific Lab.: Technical Report|url=https://digital.library.unt.edu/ark:/67531/metadc1024446/ }}</ref> For trace quantities, fume hoods with good aeration suffice; for gram amounts, [[hot cell]]s with shielding from the intense gamma radiation emitted by <sup>227</sup>Ac are necessary.<ref>{{Ullmann | first1=Cornelius |last1=Keller |first2=Walter |last2=Wolf |first3=Jashovam |last3=Shani | title = Radionuclides, 2. Radioactive Elements and Artificial Radionuclides | doi = 10.1002/14356007.o22_o15}}</ref>

==See also==
{{Portal|Chemistry}}
* [[Decay chain#Actinium series|Actinium series]]

==Notes==
{{Notelist}}

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

==Bibliography==
* {{Cite book |last1=Meyer |first1=Gerd |url=https://books.google.com/books?id=bnS5elHL2w8C&pg=PA87 |title=Synthesis of lanthanide and actinide compounds |last2=Morss |first2=Lester R. |publisher=Springer |year=1991 |isbn=0-7923-1018-7}}

==External links==
* [http://www.periodicvideos.com/videos/089.htm Actinium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+actinium,+radioactive NLM Hazardous Substances Databank – Actinium, Radioactive]
* [https://web.archive.org/web/20110825123745/http://radchem.nevada.edu/classes/rdch710/files/actinium.pdf Actinium] in {{cite book
| title = The Chemistry of the Actinide and Transactinide Elements
| editor1-last = Morss |editor2-first = Norman M.
| editor2-last = Edelstein
| editor3-last = Fuger |editor3-first = Jean
| last1 = Kirby |first1 = H. W.
| last2 = Morss |first2 = L. R.
| publisher = Springer
| date = 2006
| isbn = 978-1-4020-3555-5
| location = Dordrecht, The Netherlands
| edition = 3rd
}}

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