actinium

radium ← actinium → thorium La ↑ Ac ↓ Ute 89Ac Periodic table
Appearance
silvery
General properties
Name, symbol, number	actinium, Ac, 89
Element category	actinide
Group, period, block	n/a, 7, 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
Miscellanea
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
This box: view • talk • edit

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.

History

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 history of the discovery stayed questionable and in publications from 1971^[8] and later in 2000^[9] showed that Debierne's 1904 claims conflict with those in his 1899 and 1900 publications.

The word actinium comes from the Greek aktis, aktinos, meaning beam or ray.

Characteristics

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]

Chemistry

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]

Isotopes

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 isotopes of actinium range in atomic weight from 206 u (²⁰⁶Ac) to 236 u (²³⁶Ac).^[14]

Occurrence

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).

Applications

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] 225}Ac 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]

Precautions

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

See also

• Actinium series

References

External links

Wikimedia Commons has media related to: Actinium

Look up actinium in Wiktionary, the free dictionary.

• WebElements.com - Actinium
• NLM Hazardous Substances Databank – Actinium, Radioactive