Actinium

89 radium ← actinium → thorium La ↑ Ac ↓ Ute periodic table
General
Name, Symbol, Number	actinium, Ac, 89
Chemical series	actinides
Group, Period, Block	3, 7, f
Appearance	silvery
Atomic mass	(227) g/mol
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/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)
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·K)
CAS registry number	7440-34-8
Notable isotopes
Main article: Isotopes of actinium iso NA half-life DM DE ( MeV) DP 225Ac syn 10 days α 5.935 221 Fr 226Ac syn 29.37 hours β- 1.117 226 Th ε 0.640 226 Ra α 5.536 222 Fr 227Ac 100% 21.773 years β- 0.045 227 Th α 5.042 223 Fr
References

Actinium is a chemical element in the periodic table that has the symbol Ac and atomic number 89.

Notable characteristics

Actinium is a silvery radioactive metallic element. Due to its intense radioactivity, Actinium glows in the dark with an eerie blue light. It is found only in traces in uranium ores as 227-Ac, 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.

Applications

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

Actinium-225 is used in medicine to produce Bi-213 in a reusable generator or can be used alone as an agent for radio-immunotherapy.

History

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.

Occurrence

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

Isotopes

Naturally occurring actinium is composed of 1 radioactive isotope; ²²⁷Ac. 36 radioisotopes have been characterized with the most stable being 227-Ac with a half-life of 21.772 y, 225-Ac with a half-life of 10.0 days, and 226-Ac 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 is²¹⁷Ac which decays through alpha decay and electron capture. It has a half-life of 69 ns. Actinium also has 2 meta states.

Purified actinium-227 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 (²⁰⁶actinium) to 236 amu (²³⁶Ac).

Precautions

Actinium-227 is extremely radioactive, and in terms of its potential for radiation induced health effects, actinium-227 is about as dangerous as plutonium. Ingesting even small amounts of actinium-227 would present a serious health hazard.