Actinium . Actinium is a chemical element with symbol Ac and atomic number 89, belonging to group 3 (formerly IIIA) of the periodic table of elements. It is one of the rare earths and gives its name to one of the series, that of actinides .

It is a soft radioactive metal that glows in the dark. The known isotopes with mass number between 209 and 234, the most stable 227Ac which has a half life of 21.7 years. 227Ac is found in natural uranium in a proportion of the order of 0.175% and 228Ac is also found in nature.

There are 22 other man-made isotopes of actinium, all radioactive and all with very short half-lives. Discovered by André Louis Debierne in 1899 , its main application is as a source of alpha particles .


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  • 1 History
  • 2 Features
  • 3 Obtaining
  • 4 Applications
  • 5 Isotopes
  • 6 Health effects
  • 7 Curiosities
  • 8 Sources


Actinium was discovered in 1899 by the French chemist André Louis Debierne who obtained it from pitchblende , and characterized it as a substance similar to titanium in 1899, and thorium in 1900 . In 1902 it was discovered, independently, by Friedrich Oscar Giesel as a substance very similar to lanthanum , and named it “emanium” in 1904 . The name Actinio comes from the Greek ‘aktinos’ which means radiant or ray.

It is a soft, radioactive metal that glows in the dark. Its activity is 150 times higher than that of radium and it is applied sporadically in the analysis of trace minerals (the so-called activation analysis).

The discovery of radioactive isotopes began with the demonstration in 1912–1913 that one of the actinium products, then called actinium B, was chemically identical to lead . In the same way, another product of actinium, called actinium C, was chemically identical to bismuth . Those findings led to the conclusion that some elements contained atoms that differed in chemical activity, even though they had the same atomic number: a radioisotope .


Actinium is a metallic element, radioactive like all actinides and silver in color. Due to its intense radioactivity it glows in the dark with a bluish light. The 227Ac isotope, found only in trace amounts in the ores of uranium , is a particle emitter α and β with a half-life of 21.773 years. One ton of uranium ore contains about 0.1 g of actinium.

Its chemical behavior is very similar to that of the rest of the rare earths and particularly that of lanthanum . Actinium is also similar to radium . However, actinium does not have electrons in the 5f orbital like the rest of the actinides, but its electronic configuration is 6d17s2.


There is only a short list of compounds with actinium, for example AcF3, AcCl3, AcBr3, AcOF, AcOCl, AcOBr, Ac2S3, Ac2O3 and AcPO4. All these molecules have very similar configurations to the corresponding lanthanum compounds, so it is estimated that actin occurs in them with an oxidation number of +3.

Traces of actinium (227Ac) are found in uranium ores , but small amounts (on the order of milligrams) are commonly obtained by bombarding 226Ra with neutrons in a nuclear reactor followed by a β- decay of the resulting 227Ra isotope.

The metal is also made by reducing actinium fluoride with lithium , magnesium, or calcium vapor at 1100–1300 ° C. Actinium is also obtained from the disintegration of 235U and the uranitita (U3O8), a major uranium. The first artificial production of actinium took place at the Argonne National Laboratory in Chicago .


Its radioactivity is of the order of 150 times that of radium, making it useful as a source of neutrons; aside from this, it has no significant industrial applications. Ac-225 is used in medicine in the production of Bi-213 for radiotherapy . The francium , element 87 of the periodic table, a metal radioactive alkaline characterized in 1939 , which is obtained in small amounts as a result of a specific decay of the radioactive series 227Ac in having start with 235U.


Thirty unstable isotopes, whose half-lives range from 69 nanoseconds of 217-Ac to 21,773 years of 227-Ac. The 228-Ac (6.15 hours) receives the name of “mesotorio 2”.

The radioactive isotopes 227Ac are the only ones found in nature and are the most stable of the thirty isotopes identified with a half-life of 21.773 years, followed by 225Ac (10 days), 226Ac (29.37 hours) and the 228Ac (6.13 hours). The rest of the isotopes have half-lives of less than 10 hours and most of them less than one minute.

227Ac reaches equilibrium with its decay products after 185 days, subsequently transmuting according to a half-life of 21,773 years.

225Ac is used in medicine in the production of Bi-213 used in radiotherapy. The combination of the 225Ac isotope with the monoclonal antibody lintuzumab forms an alpha-radiation-emitting radioimmune conjugate (abbreviated “225Ac-HuM195”) with possible antineoplastic activity.

The fraction corresponding to the monoclonal antibody lintuzumab binds specifically to the cell surface antigen CD33 and, with the presence of radioactive actinium, delivers a dose of alpha radiation to the malignant cell that is cytotoxic for cells that express said cell antigen, mainly stem cells non-pluripotent normal hematopoietic cells and turns out to be overexpressed in cells of myeloid leukemia causative agents.

In the same way, 213Bi – produced from 225Ac itself – is combined with the monoclonal antibody with the same radioimmune effect. The use of both isotopes avoids having to use beta emitters as was done in the past, which injured healthy tissue surrounding the tumor. The combination with 225Ac turns out to have higher potency because it has a higher half life than 213Bi.

Health effects

227Ac is extremely radioactive and, considering its potential health effects, is just as dangerous as plutonium . Ingestion, even in small amounts, can cause very serious damage.


Actinium is only found as an intermediate product in the radioactive decay series and represents 5.5×10-14% by weight of the crust; 227-Ac, the decay product of 235-U, is a beta emitter with a half-life of 21.8 years. In nature it appears associated with uranium minerals: 1.5×10-6% by weight in pitchblende. Therefore, it is very rare. The main decay products of 227-Ac are 227-Th (18.7 days), 223-Ra (11.4 days), and others with a shorter half-life, including isotopes of radon, bismuth, and polonium. and lead; in equilibrium with its decay products is a source of alpha rays.

The metal has been prepared by reduction of actinium fluoride (AcF3) with lithium vapor at 1100-1300ºC or by radiation irradiation in nuclear reactors according to the process: 226-Ra (n, g) 227-Ra —> 227 -Ac + b It is a silvery white heavy metal. It rusts immediately in air. The chemical properties are similar to those of lanthanides, particularly lanthanum.

The purified actinium reaches equilibrium with its decay products in 185 days and then decays according to its half-life of 21.8 years. It is 150 times more active than radium, being used in the production of neutrons.


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