- Actinium (Ac) is a soft, silvery-white, highly radioactive metal with atomic number 89, positioned in Group 3 of the periodic table and considered the first element in the actinide series.
- Its electron configuration is [Rn] 6d¹ 7s², and it predominantly forms Ac³⁺ ions in chemical compounds. The atomic structure contains eighty-nine protons, typically one hundred and thirty-eight neutrons in its most common isotope, and eighty-nine electrons arranged in seven shells.
- Naturally occurring actinium consists almost entirely of the isotope actinium-227 (²²⁷Ac), which has a half-life of about 21.8 years and undergoes both alpha and beta decay. Trace amounts of actinium-228 (²²⁸Ac) occur as part of the thorium decay series.
- Actinium is extremely rare in nature, found in trace amounts in uranium and thorium ores at concentrations of about 0.15 milligrams per ton. It is more commonly produced artificially by neutron irradiation of radium-226 in nuclear reactors. Because of its scarcity and intense radioactivity, actinium has no large-scale commercial production and is primarily used for research and medical applications.
- The element was discovered in 1899 by German chemist Friedrich Oskar Giesel, who isolated it from uranium ore. Its name is derived from the Greek word “aktinos,” meaning “ray” or “beam,” in reference to the intense radiation it emits. Actinium was the first non-uranium element to be discovered as radioactive.
- Actinium’s most notable application is in medicine, particularly in targeted alpha-particle cancer therapy. The isotope actinium-225 (²²⁵Ac) is used in experimental treatments to deliver highly localized alpha radiation to tumors while minimizing damage to surrounding healthy tissue. Actinium-227 is also used as a neutron source when combined with beryllium.
- Chemically, actinium behaves similarly to lanthanum, its lighter homolog, but is more reactive due to its larger atomic radius and intense radioactivity. It tarnishes rapidly in air, forming a white oxide layer, and reacts readily with oxygen, moisture, and most acids, though it is resistant to attack by hydrofluoric acid due to the formation of an insoluble fluoride.
- Biologically, actinium has no natural role in organisms and is highly toxic due to its strong radioactivity. Exposure, even in microscopic amounts, poses severe health hazards, including radiation sickness and increased cancer risk.
- From an environmental standpoint, actinium in natural settings is present only in trace amounts, and its impact is minimal compared to other radioactive contaminants. However, waste containing synthetic actinium must be handled and stored under strict radiological safety protocols.
