aktinium

Actinium is a chemical element with the symbol Ac and atomic number 89. It is a silvery-white, radioactive metal and the first member of the actinide series. Actinium exists only in trace amounts in nature, mainly in uranium ores as a decay product of uranium-235. In the laboratory it can be produced by irradiation in nuclear reactors or accelerators and is isolated from radioactive material through chemical processing.

Chemically, actinium is typically trivalent, forming Ac3+ ions in solution. Its chemistry resembles that of the lanthanides in many respects, but its compounds are intensely radioactive and can be more difficult to study. Common compounds include Ac2O3, actinium nitrate, and various oxides and halides. Actinium compounds are usually highly reactive and require careful handling and shielding.

Discovery and name: Actinium was identified in 1899 by the French chemist André-Louis Debierne, who isolated a highly radioactive residue from pitchblende. The name derives from the Greek aktis, meaning ray or beam, in reference to its radioactivity and energetic emissions.

Isotopes and occurrence: Actinium has no stable isotopes. The most long-lived natural isotope is actinium-227, with a half-life of about 21.8 years, found only in trace amounts as part of the uranium-235 decay chain. A range of shorter-lived isotopes exists, and synthetic isotopes such as actinium-225 are used in medicine.

Applications and safety: Actinium is used mainly in scientific research and in specialized medical radiopharmaceuticals, notably actinium-225 for targeted alpha-particle therapy. Because of its high radioactivity, handling requires specialized facilities, shielding, and regulatory controls.