Actinium

Actinium (from the Greek ακτις, ακτινoς, luminous ray) is a chemical element with symbol Ac and atomic number 89, belonging to group IIIB, period 7 and block D of the periodic table of elements. It is one of the rare earths and gives its name to one of the series, the actinide series.. It is a soft radioactive metal that glows in the dark. Isotopes with mass numbers between 209 and 234 are known, the most stable being ²²⁷Ac, which has a half-life of 21.7 years. ²²⁷Ac occurs in natural uranium in a proportion of the order of 0.175%, and ²²⁸Ac also occurs in nature. There are 22 other artificial 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.

Main features

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 isotope ²²⁷Ac, found only in trace amounts in uranium ores, is an emitter of α and β particles 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 lanthanum, the element just above it on the periodic table. Actinium is also similar to radium, the element that precedes it. However, actinium does not have electrons in the 5f orbital like the rest of the actinides, but its electronic configuration is 6d¹7s². found related to a coordination number of 4, is 126.0 pm.

History

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 to 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. Comparisons between these substances in 1904 were determined to be identical, and Debierne's proposed name was retained as it took precedence. Three other elements were discovered between 1898 and 1900.: polonium and radium (by Marie and Pierre Curie) and radon, a gas released during the radioactive decay of some heavier elements discovered in 1900 by the German chemist Friedrich Ernst Dorn (1848–1916).

The discovery of radioactive isotopes began with the demonstration in 1912–1913 that one of the products of actinium, then called actinium B, was chemically identical to lead. Likewise, another product of actinium, called actinium C, was chemically identical to bismuth. These 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.

Abundance and obtaining

Only a short list of compounds with actinium exists, 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 actinium occurs in them with an oxidation number of +3.

Trace amounts 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 β-decay - of the resulting isotope ²²⁷Ra.

88226Ra+01nΔ Δ 88227Ra→42,2minβ β − − 89227Ac{displaystyle mathrm {^{226}_{ 88}Ra + _{0}{1}n longrightarrow _{ 88}{227}Ra {xrightarrow[{42,2 min}]}{beta {^-}}}{{89}{227}Ac} }

Times are half-life.

The metal is also obtained by reducing actinium fluoride with lithium, magnesium, or calcium vapor at 1,100–1,300 °C. Actinium is also obtained from the decay of ²³⁵U, as well as uranitite (U₃O₈), one of the main uranium minerals. The first artificial production of actinium took place at the Argonne National Laboratory in Chicago.

Isotopes

Spectral lines of the actinium.

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 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.

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

Applications

The use of actinium is almost exclusively for scientific research. The radioactivity of actinium is on the order of 150 times that of radium, making it useful as a source of neutrons; Apart from that, it has no significant industrial applications.

Francium, element 87 of the periodic table, is a radioactive alkali metal characterized in 1939, which is obtained in small quantities as a result of a specific decay of ²²⁷Ac in the radioactive series that it starts with the 235U.

Use in medicine

²²⁵Ab is used in medicine in the production of Bi-213 used in radiotherapy. The combination of the isotope ²²⁵Ab with the monoclonal antibody lintuzumab forms a alpha-radiation-emitting radioimmunoconjugate (abbreviated “225Ac-HuM195”) with possible antineoplastic activity. The fraction corresponding to the monoclonal antibody lintuzumab binds specifically to the CD33 cell surface antigen and, in the presence of radioactive actinium, delivers a dose of alpha radiation to the malignant cell that is cytotoxic to cells that express said cell antigen, mainly stem cells. normal non-pluripotent hematopoietic cells and turns out to be overexpressed in the cells of those causing myeloid leukemia. In the same way, ²¹³Bi — produced from ²²⁵Ab itself — is combined to 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 damaged healthy tissue surrounding the tumor. The combination with ²²⁵Ac turns out to be more potent because it has a longer half-life than ²¹³Bi.

Precautions

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