Actinium

{ syn. }

100 %

In traces

Actinium ( Latinized from Greek ακτίνα AKTINA, Ray ') is a radioactive chemical element with the atomic symbol Ac and atomic number 89, the element is a metal and is part of the seventh period, d- block. It is the namesake of the actinide group, who gave him the following 14 elements.

7.1 oxides
7.2 halides
7.3 Other compounds

History

Actinium was discovered in 1899 by the French chemist André- Louis Debierne which it. Pitchblende isolated and initially ascribed to him similar to the titanium or the thorium Friedrich Giesel discovered actinium matter in 1902 and described a similarity to lanthanum; in 1904, he named it " emanium ". After comparing the substances in 1904 Debiernes naming was given preference because he had discovered it first.

The history of the discovery was still described in publications of 1971 and later in 2000 as questionable. They show that the publications of 1904 on the one hand and the of 1899 and 1900 on the other hand have contradictions.

Production and representation

Since little Actinium is present in uranium ores, this source does not matter for the extraction. Technically, the isotope 227Ac by irradiation of 226Ra with neutrons in nuclear reactors is produced.

The rapid decay of actinium only small amounts were always available. The first artificial production of actinium was performed in the Argonne National Laboratory in Chicago.

Properties

Physical Properties

The metal is silver white shiny and relatively soft. Due to its high radioactivity, actinium glows in the dark in a bright blue light.

Actinium is the eponymous element of the actinide elements, similar to lanthanum for the lanthanides. The group of elements shows marked differences as the lanthanides; Therefore, it took until 1945 until Glenn T. Seaborg was able to propose the most important changes to the periodic table of Mendeleev: the introduction of the actinides.

Chemical Properties

It is very reactive and is attacked by air and water, but becomes covered with a layer of Actiniumoxid, whereby it is protected from further oxidation. The Ac3 ion is colorless. The chemical behavior of actinium is very similar to lanthanum. Actinium is trivalent in all ten known compounds.

Isotopes

Known are 26 isotopes, of which only two occur naturally. The longest-lived isotope 227Ac (half-life 21.8 years ) is an alpha-and beta emitters. It is a decay product of uranium isotope 235U and comes to a small part in uranium ores before. From this, ponderable quantities 227Ac win, which thus enable a relatively simple study of this element. Since there are some gamma emitters among the radioactive decay products, but consuming radiation protection measures are necessary.

Use

Actinium is used for the production of neutrons, which play a role in activation analysis. In addition, it is used for the thermionic energy conversion.

The decay of 227Ac is dual: While most of the emission of beta particles passes into the thorium isotope 227th, breaks down about 1% by alpha emission to 223Fr. A solution of 227Ac is therefore useful as a source for the short-lived Franciumisotop 223Fr. The latter can then be periodically removed and examined.

Safety

Classifications according to the Hazardous Substances Ordinance are not available because they only include the chemical danger and play a very minor role compared to the risks based on the radioactivity. Even the latter applies only if there is a relevant material for this amount.

Compounds

Only a small number of known Actiniumverbindungen including ACF3, AcCl3, AcBr3, ACOF, AcOCl, AcOBr, Ac2S3, Ac2O3 and AcPO4. Except AcPO4 they are all similar to the corresponding lanthanum and actinium contained in the oxidation state 3. In particular, the lattice constants of the respective lanthanum and actinium compounds that differ only in a few percent.

Oxides

Actiniumoxid ( Ac2O3 ) can be obtained by heating the hydroxide at 500 ° C or oxalate at 1100 ° C in vacuum. The crystal lattice is isotypic with the oxides of most trivalent rare earth metals.

Halides

Actiniumtrifluorid can be presented in solution or by solid state reaction either. In the first case are added at room temperature to a hydrofluoric acid Ac3 solution and the product precipitates out. in the other case Actinium metal is treated with hydrogen fluoride at 700 ° C in a platinum apparatus. The implementation of Actiniumtrifluorid with moist ammonia at 900-1000 ° C provides the oxyfluoride ACOF. While Lanthanoxifluorid easily generated by burning lanthanum trifluoride in air at 800 ° C in about an hour, gives a similar treatment of Actiniumtrifluorid no ACOF and only leads to a melt of the original substance.

Actiniumtrichlorid is obtained by reaction of Actiniumhydroxid or oxalate with carbon tetrachloride at temperatures above 960 ° C. Similar to the oxyfluoride Actiniumoxichlorid AcOCl can be manufactured at 1000 ° C by hydrolysis of Actiniumtrichlorid with wet ammonia. But unlike the oxyfluoride the oxychloride can also be displayed from a solution of Actiniumtrichlorid in hydrochloric acid with ammonia.

The reaction of aluminum bromide and Actiniumoxid leads to Actiniumtribromid:

And treatment with moist ammonia at 500 ° C leads to Oxibromid AcOBr.