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General properties
Name, symbol, number actinium, Ac, 89
Element category actinide
Group, period, block n/a7, f
Standard atomic weight (227)g·mol−1
Electron configuration [Rn] 6d1 7s2
Electrons per shell 2, 8, 18, 32, 18, 9, 2 (Image)
Physical properties
Phase solid
Density (near r.t.) 10 g·cm−3
Melting point (circa) 1323 K, 1050 °C, 1922 °F
Boiling point 3471 K, 3198 °C, 5788 °F
Heat of fusion 14 kJ·mol−1
Heat of vaporization 400 kJ·mol−1
Specific heat capacity (25 °C) 27.2 J·mol−1·K−1
Atomic properties
Oxidation states 3
(neutral oxide)
Electronegativity 1.1 (Pauling scale)
Ionization energies 1st: 499 kJ·mol−1
2nd: 1170 kJ·mol−1
Covalent radius 215 pm
Crystal structure face-centered cubic
Magnetic ordering no data
Thermal conductivity (300 K) 12 W·m−1·K−1
CAS registry number 7440-34-8
Most stable isotopes
Main article: Isotopes of actinium
iso NA half-life DM DE (MeV) DP
225Ac syn 10 days α 5.935 221Fr
226Ac syn 29.37 hours β 1.117 226Th
ε 0.640 226Ra
α 5.536 222Fr
227Ac 100% 21.773 years β 0.045 227Th
α 5.042 223Fr

Actinium (pronounced /ækˈtɪniəm/, ak-TIN-nee-əm) is a radioactive chemical element with the symbol Ac and atomic number 89, which was discovered in 1899. It was the first non-primordial radioactive element to be isolated. Polonium, radium and radon were observed before actinium, but they were not isolated until 1902. Actinium gave the name to the actinoid series, a group of 15 similar elements between actinium and lawrencium in the periodic table.



André-Louis Debierne, a French chemist, announced the discovery of a new element in 1899. He separated it from pitchblende and described the substance (in 1899) as similar to titanium[1] and (in 1900) as similar to thorium.[2] Friedrich Oskar Giesel independently discovered actinium in 1902[3] as a substance being similar to lanthanum and called it "emanium" in 1904.[4] After a comparison of substances in 1904,[5] Debierne's name was retained because it had seniority.[6][7]

The stated history of the discovery of actinium remained questionable for decades. In publications starting in 1971[8] and continuing especially in 2000[9], it was shown that Debierne's published results in 1904 conflict with those in his articles published in 1899 and 1900.

The word actinium comes from the Greek aktis, aktinos (ακτίς, ακτίνος), meaning beam or ray.


Actinium is a silvery, radioactive, metallic element. Due to its intense radioactivity, actinium glows in the dark with a pale blue light. The chemical behavior of actinium is similar to that of the rare earth element lanthanum.[10]



Actinium shows similar chemical behavior to lanthanum. Due to this similarity the separation of actinium from lanthanum and the other rare earth elements, which are also present in uranium ores was difficult. Solvent extraction and ion exchange chromatography was used for the separation.[11] Only a limited number of actinium compounds are known, for example AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3 and AcPO4. All the mentioned compounds are similar to the corresponding lanthanum compounds and show that actinium compounds are generally in the oxidation state of +3.[12]

Relationship with actinoids

Actinium is the first element of the actinoids and gave the group its name, similar to lanthanum for the lanthanoids. The group of elements is more diverse than the lanthanoids and therefore it took until 1945 when Glenn T. Seaborg proposed the most significant change to Mendeleev's periodic table, by introducing the actinoids.[13]


Naturally occurring actinium is composed of 1 radioactive isotope; 227Ac. 36 radioisotopes have been characterized with the most stable being 227Ac with a half-life of 21.772 y, 225Ac with a half-life of 10.0 days, and 226Ac with a half-life of 29.37 h. All of the remaining radioactive isotopes have half-lives that are less than 10 hours and the majority of these have half-lives that are less than 1 minute. The shortest-lived isotope of actinium is 217Ac which decays through alpha decay and electron capture. It has a half-life of 69 ns. Actinium also has 2 meta states.[14]

Purified 227Ac comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.773-year half-life; the successive decay products are part of the actinium series. The isotopes of actinium range in atomic weight from 206 u (206Ac) to 236 u (236Ac).[14]


Actinium is found in trace amounts in uranium ore, but more commonly is made in milligram amounts by the neutron irradiation of 226Ra in a nuclear reactor. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300°C.[10]

Actinium is found only in traces in uranium ores as 227Ac, an α and β emitter with a half-life of 21.773 years. One ton of uranium ore contains about a tenth of a gram of actinium. The actinium isotope 227Ac is a transient member of the actinium series decay chain, which begins with the parent isotope 235U (or 239Pu) and ends with the stable lead isotope 207Pb. Another actinium isotope (225Ac) is transiently present in the neptunium series decay chain, beginning with 237Np (or 233U) and ending with near-stable bismuth (209Bi).


It is about 150 times as radioactive as radium, making it valuable as a neutron source for energy. Otherwise it has no significant industrial applications.[15]

225Ac is used in medicine to produce 213Bi in a reusable generator or can be used alone as an agent for radio-immunotherapy for Targeted Alpha Therapy (TAT).[16] 225Ac was first produced artificially by the Institute for Transuranium Elements (ITU) in Germany using a cyclotron and by Dr Graeme Melville at St George Hospital in Sydney using a linac in 2000.[17]


227Ac is extremely radioactive, and in terms of its potential for radiation induced health effects[18] 227Ac is even more dangerous than plutonium. Ingesting even small amounts of 227Ac would be fatal.[citation needed]

See also


  1. ^ Debierne, André-Louis (1899). "Sur un nouvelle matière radio-active" (in French). Comptes rendus 129: 593–595. 
  2. ^ Debierne, André-Louis (1900-1901). "Sur un nouvelle matière radio-actif - l'actinium" (in French). Comptes rendus 130: 906–908. 
  3. ^ Giesel, Friedrich Oskar (1902). "Ueber Radium und radioactive Stoffe" (in German). Berichte der Deutschen Chemische Geselschaft 35 (3): 3608–3611. doi:10.1002/cber.190203503187. 
  4. ^ Giesel, Friedrich Oskar (1904). "Ueber den Emanationskörper (Emanium)" (in German). Berichte der Deutschen Chemische Geselschaft 37 (2): 1696–1699. doi:10.1002/cber.19040370280. 
  5. ^ Debierne, André-Louis (1904). "Sur l'actinium" (in French). Comptes rendus 139: 538–540. 
  6. ^ Giesel, Friedrich Oskar (1904). "Ueber Emanium" (in German). Berichte der Deutschen Chemische Geselschaft 37 (2): 1696–1699. doi:10.1002/cber.19040370280. 
  7. ^ Giesel, Friedrich Oskar (1905). "Ueber Emanium" (in German). Berichte der Deutschen Chemische Geselschaft 38 (1): 775–778. doi:10.1002/cber.190503801130. 
  8. ^ Kirby, H. W. (1971). "The Discovery of Actinium". Isis 62 (3): 290–308. doi:10.1086/350760. 
  9. ^ Adloff, J. P. (2000). "The centenary of a controversial discovery: actinium". Radiochim. Acta, 88: 123–128. doi:10.1524/ract.2000.88.3-4.123. 
  10. ^ a b Stites, Joseph G.; Salutsky, Murrell L.; Stone, Bob D. (1955). "Preparation of Actinium Metal". J. Am. Chem. Soc. 77 (1): 237–240. doi:10.1021/ja01606a085. 
  11. ^ Katz, J. J.; Manning, W M (1952). "Chemistry of the Actinide Elements Annual Review of Nuclear Science". Annual Review of Nuclear Science 1: 245–262. doi:10.1146/annurev.ns.01.120152.001333. 
  12. ^ Sherman, Fried; Hagemann, French; Zachariasen, W. H. (1950). "The Preparation and Identification of Some Pure Actinium Compounds". Journal of the American Chemical Society 72: 771–775. doi:10.1021/ja01158a034. 
  13. ^ Seaborg, Glenn T. (1946). "The Transuranium Elements". Science 104 (2704): 379–386. doi:10.1126/science.104.2704.379. PMID 17842184. 
  14. ^ a b Audi, Georges (2003). "The NUBASE Evaluation of Nuclear and Decay Properties". Nuclear Physics A (Atomic Mass Data Center) 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001. 
  15. ^ Dixon, W.R. (1957). "Neutron Spectrum of an Actinium–Beryllium Source". Can. J. Phys./Rev. Can. Phys. 35 (6): 699–702. 
  16. ^ Bolla, Rose A.; Malkemus, D; Mirzadeh, S (2005). "Production of actinium-225 for alpha particle mediated radioimmunotherapy". Applied Radiation and Isotopes 62 (5): 667–679. doi:10.1016/j.apradiso.2004.12.003. PMID 15763472. 
  17. ^ Melville, G; Allen, Bj (Apr 2009). "Cyclotron and linac production of Ac-225.". Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine 67 (4): 549–55. doi:10.1016/j.apradiso.2008.11.012. ISSN 0969-8043. PMID 19135381. 
  18. ^ Langham, W. (1952). "Toxicology of Actinium Equilibrium Mixture". Los Alamos Scientific Lab.: Technical Report. doi:10.2172/4406766. 

External links


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also actinium



Actinium n

  1. (chemistry) chemical element actinium (atomic number 89)

See also

Simple English

Actinium is chemical element 89 on the periodic table. Its symbol is Ac. Actinium's mass is 227 g/mol.

Actinium is a silver radioactivesolid metal. It is so radioactive that it glows in the dark. Even a small amount of actinium is dangerous to people.

Actinium was discovered in 1899 by André-Louis Debierne, a French chemist.


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