2007 Schools Wikipedia Selection. Related subjects: Chemical elements
|Name, Symbol, Number||actinium, Ac, 89|
|Group, Period, Block||3, 7, f|
|Atomic mass||(227) g/mol|
|Electron configuration||[Rn] 6d1 7s2|
|Electrons per shell||2, 8, 18, 32, 18, 9, 2|
|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|
|Heat capacity||(25 °C) 27.2 J·mol−1·K−1|
|Crystal structure||cubic face centered|
|Electronegativity||1.1 (Pauling scale)|
|Ionization energies||1st: 499 kJ/mol|
|2nd: 1170 kJ/mol|
|Atomic radius||195 pm|
|Magnetic ordering||no data|
|Thermal conductivity||(300 K) 12 W·m−1·K−1|
|CAS registry number||7440-34-8|
Actinium is a silvery radioactive metallic element. Due to its intense radioactivity, Actinium glows in the dark with a pale blue light. It 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.
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.
Actinium was discovered in 1899 by André-Louis Debierne, a French chemist, who separated it from pitchblende. Friedrich Otto Giesel independently discovered actinium in 1902. The chemical behaviour of actinium is similar to that of the rare earth lanthanum.
The word actinium comes from the Greek aktis, aktinos, meaning beam or ray.
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 1300ºC.
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 amu (206Ac) to 236 amu (236Ac).
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 present a serious health hazard.