|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/cm³|
|Melting point||(circa) 1323 K
(1050 °C, 1922 °F)
|Boiling point||3471 K
(3198 °C, 5788 °F)
|Heat of fusion||14 kJ/mol|
|Heat of vaporization||400 kJ/mol|
|Heat capacity||(25 °C) 27.2 J/(mol·K)|
|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·K)|
|CAS registry number||7440-34-8|
Actinium (chemical symbol Ac, atomic number 89) is a silvery, radioactive, metallic element. Due to its intense radioactivity, it glows in the dark with a pale blue light. It is about 150 times as radioactive as radium and is therefore a valuable source of neutrons. Its isotope 225Ac is used in nuclear medicine.
Actinium is found in trace amounts in uranium ore, but it is more commonly 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 ºC.
The word actinium comes from the Greek aktis, aktinos, meaning beam or ray.
Actinium is often considered as the first of the actinides, which are a group of "inner transition metals." From the standpoint of their electronic structure, the actinides are characterized by the gradual filling of the 5f subshell. Actinium, however, has no electrons in its 5f subshell, and it best fits with the elements of group three.
Naturally occurring actinium is composed of one 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 ten days, and 226Ac with a half-life of 29.37 h. All of the remaining radioactive isotopes have half-lives that are less than ten hours and the majority of these have half lives that are less than one 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 two 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).
Actinium 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.
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.
All links retrieved November 3, 2019.
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