Actinium

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89 radium ← actinium → thorium
La

Ac

Ute
Periodic Table - Extended Periodic Table
General
Name, Symbol, Number actinium, Ac, 89
Element category actinides
Group, Period, Block 3, 7, f
Appearance silvery
Standard atomic weight (227)  g·mol−1
Electron configuration [Rn] 6d1 7s2
Electrons per shell 2, 8, 18, 32, 18, 9, 2
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
Crystal structure cubic face centered
Oxidation states 3
(neutral oxide)
Electronegativity 1.1 (Pauling scale)
Ionization energies 1st: 499 kJ/mol
2nd: 1170 kJ/mol
Atomic radius 195  pm
Miscellaneous
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
References

Actinium (pronounced /ækˈtɪniəm/) is a chemical element with the symbol Ac and atomic number 89.

Contents

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 lanthanum.

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. Otherwise it has no significant industrial applications.

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). 225Ac was first produced artificially by the ITU in Germany using a cyclotron and by Dr Graeme Melville at St George Hospital in Sydney using a linac in 2000.

History

Actinium was discovered in 1899 by André-Louis Debierne, a French chemist, who separated it from pitchblende as a substance being similar to titanium (1899) or similar to thorium (1890). Friedrich Oskar Giesel independently discovered actinium in 1902 as a substance being similar to lanthanum and called it "emanium" in 1904. After a comparison of substances in 1904, Debierne's name was retained because it had seniority.

The history of the discovery stayed questionable and in publications from 1971 and later in 2000 showed that the claims of André-Louis Debierne in 1904 conflict with the publications in 1899 and 1890.

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

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.

Isotopes

Main article: isotopes of actinium

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-lifes that are less than 10 hours and the majority of these have half lifes 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.

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).

Precautions

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

Fictional Applications

Actinium compounds, along with advanced circuitry are used in a time travel device in Excalibur: Morgana's Revenge