Actinium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

89 radium ← actinium → thorium La ↑ Ac ↓ Ute Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	actinium, Ac, 89
Chemical series	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
Selected 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.

Notable characteristics

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.

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. Friedrich Oskar Giesel independently discovered actinium in 1902 and called it "emanium" in 1904. Debierne's name was retained because it had seniority. 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 ²²⁶Ra 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 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.