AC

Actinium (Ac) is a chemical element with atomic number 89. It is the first member of the actinide series and is a highly radioactive silvery-white metal.

In nature, actinium is extremely scarce. Trace amounts are found in uranium and thorium ores and in the decay chains of these elements. It can also be produced artificially in reactors or particle accelerators by irradiating radium, thorium, or other materials. Natural activity is dominated by the isotope Ac-227.

Actinium is highly radioactive and converts to other elements through alpha decay. The most long-lived natural isotope is Ac-227, with a half-life of about 21.8 years; many other isotopes have much shorter half-lives and are produced in laboratories. The element is studied primarily for scientific research and medicinal applications involving its radioactive isotopes.

Chemically, actinium predominantly exhibits the +3 oxidation state and forms compounds such as Ac2O3 and AcCl3. Its chemistry is broadly similar to the lanthanides, but it is classified as part of the actinide series. In practice, actinium chemistry is explored mainly in specialized radiochemical and materials research settings.

Applications of actinium isotopes are largely in research and development. Actinium-225, for example, is investigated as a source of alpha particles for targeted cancer therapies. Because of its radioactivity, actinium requires stringent shielding and handling precautions and is typically used under controlled, laboratory conditions.

Discovery and naming: actinium was identified in 1899 by André Debierne and is named from the Greek aktis, meaning ray.