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General Info
Atomic Symbol Atomic symbol::Ac
Atomic Number Atomic number::89
Atomic Weight Atomic weight::227.0278 g/mol
Chemical series Actinide
Appearance Actinium sample.jpg
Group, Period, Block IIIB, 7, f
Electron configuration [Rn] 6d1, 7s2
Electrons per shell 2,8,18,32,18,9,2
Electron shell actinium.png
CAS number CAS number::7440-34-8
Physical properties
Phase Solid
Density Density::10.07 g/ml
Melting point Melting point::1050° C
Boiling point Boiling point::3199° C
Isotopes of Actinium
iso NA half-life DT DE (MeV) DP
206Ac syn 11 ms α
206mAc syn 22 ms α
206m2Ac syn 33 ms α
207Ac syn 27 ms α 203Fr
208Ac syn 95 ms α + ε 204Fr;208Ra
208mAc syn 25 ms α + ε 204Fr;208Ra
209Ac syn 0.10 s α + ε 205Fr;209Ra
210Ac syn 0.35 s α + ε 206Fr;210Ra
211Ac syn 0.25 s α 207Fr
212Ac syn 0.93 s α + ε 208Fr
213Ac syn 0.80 s α 209Fr
214Ac syn 8.2 s α + ε 210Fr
215Ac syn 0.17 s α + ε 211Fr
216Ac syn 0.33 ms α 212Fr
217Ac syn 69 ns α + ε 213Fr
218Ac syn 1.08 µs α 214Fr
219Ac syn 11.8 µs α 215Fr
220Ac syn 26.4 ms α + ε 216Fr
221Ac syn 52 ms α 217Fr
222Ac syn 5 s α + ε 218Fr
222mAc syn 63 s α + ε 218Fr
223Ac syn 2.10 min α + ε 219Fr;223Ra
224Ac syn 2.78 h α + ε + β- 220Fr;224Ra;224Th
225Ac syn 10 d α 221Fr
226Ac syn 29.37 h α + ε + β- 222Fr;226Ra;226Th
227Ac 100% 21.772 y α + β- 224Fr;228Th
228Ac syn 6.15 h β- 229Th
229Ac syn 62.7 min β- 229Th
230Ac syn 122 s β- 230Th
231Ac syn 7.5 min β- 231Th
232Ac syn 119 s β- 232Th
233Ac syn 145 s β- 233Th
234Ac syn 44 s β- 234Th
235Ac syn 40 s β- 235Th
236Ac syn 2 min β- 236Th
All properties are for STP unless otherwise stated.

Actinium is a chemical element that is classified as a transition metal and the first element in the actinide series. Discovered in 1899 by André-Louis Debierne, it was named actinium for the Greek word for beam, aktis.[1] On the Periodic table, it is located in Group IIIB and period 7.It is among the f block of elements, meaning that all of its valence electrons are in the f sublevel. As a transition metal, it bears metallic properties that vary widely from other transition metals. It is only found in trace amounts in samples of uranium ore.[2] Like many larger elements, it is highly radioactive and can be hazardous for one's health.[3] Its longest lasting isotope, 227Ac, has a half life of 21.773 years. This is relatively short amongst normal elements, but very long among elements with higher atomic mass. [2]


Actinium emits blue light because of its radioactive nature.

Actinium, while only existing in small quantities, has several measurable properties.It exists as a heavy, silvery metal that is extremely radioactive.[4] It has no stable isotopes, which explains its rareness in nature. Its primary method of decay is alpha decay.[1] It's physical properties are actually very similar to lanthanum and radium, the elements adjacent to it in the periodic table. This could be attributed to the similar number of valence electrons, which determine an atom's physical and bonding properties.[5] It has a boiling point that is neither extremely high or low among the elements of the periodic table at 1050° C.[6] Actinium's atomic weight of 227 indicates that it is neutron rich, bearing almost twice as many neutrons on average as protons. It has an oxidation state of 3+, but few compounds have been successfully created with it.[1]



Actinium is very rare in nature. It has only been discovered naturally in uranium ore (pitchblende). It is naturally the product of U-235 decay. Even in uranium ore it exists in very small quantities. For every pound of uranium ore, there is approximately 1.65x10-7 pounds of actinium.[2] The only isotope that occurs naturally is 227Ac.[5] In comparison with other elements it makes up a microscopic portion of the earth's crust. There is approximately 5.5x10-10 mg for every kg of matter. [1]


Actinium is also produced synthetically. This is accomplished by bombarding radium atoms with neutrons. The neutrons cause the radium to become unstable and decay into actinium. Because of the quantities that can be produced compared to naturally extracting it from uranium, this is the primary method of obtaining actinium samples. Most actinium produced this way is used for research purposes.[5]


Because of its rareness in nature, actinium is primarily produced in particle accelerators such as the Large Hadron Collider.
Actinium has no uses so far. Its only application has been in research. Even among the research samples, only actinium of 98% purity can be used. Further research may reveal potential applications.[5] It has been speculated, however, that it could be used in the production of neutrons. Since actinium is neutron rich and unstable, the shedded neutrons could be used in the production of other elements. As actinium is created by bombarding radium with neutrons, so could other particles be created with actinium's neutrons.[1]

Other possible uses include:

  • Use in thermal electric generators for spacecraft
  • Source of radiation in cancer radiation therapy - There are several isotopes of actinium that could be used for this, but, while many kill cancer cells, they will also accumulate in the bones and liver. While solving the temporary problem of one type of cancer, they may very well cause future cancers because of radioactive emissions.[3]

The Actinide Series

Actinium is the first element in the actinide series of elements on the periodic table. The actinide series stretches from actinium to lawrencium. They are all located in the seventh series and are in the f-block of the periodic table. All members of the actinide series are unstable and are extremely radioactive. They are also very electropositive, meaning that they easily give up electrons in the few bonds that they can form. They primarily combine with nonmetals. Upon being exposed to air, all actinides readily tarnish, losing their lustrous appearance. All the elements show relatively short half lives for radioactive elements.[7]


  1. 1.0 1.1 1.2 1.3 1.4 Gagnon, Steve. The Element Actinium Jefferson Lab. Web. Accessed 10/29/2011.
  2. 2.0 2.1 2.2 Author Unknown. Actinium Element Facts Chemicool. Web. Accessed 10/29/2011.
  3. 3.0 3.1 Author Unknown. Actinium Elements Database. Web. Accessed 11/15/2011.
  4. Author Unknown. Actinium Facts Web. Accessed 10/29/2011.
  5. 5.0 5.1 5.2 5.3 Author Unknown. Actinium BookRags. Web. Accessed 10/30/2011.
  6. Author Unknown. Chemical elements listed by melting point Lenntech. Web. Accessed 11/2/2011.
  7. Author Unknown. Actinides-Properties of Element Groups Web. Accessed 11/15/2011.