An Overview about the Chemical Element Actinium


Symbol: Ac

Atomic Number: 89

Atomic Mass: 227.0 amu (atomic mass units)

Melting Point: 1050.0 C (1323.15 K, 1922.0 F)

Boiling Point: 3200.0 C (3473.15 K, 5792.0 F)

Number of Protons: 89

Number of Electrons: 89

Number of Neutrons: 138

Classification: Rare Earth Metal

Crystal Structure: Cubic

Density @ 293 K: 10.07 grams per cubic centimeter

Color: Silver

The highly radioactive element actinium was discovered by the French chemist Andre-Louis Debierne in 1899 in Paris, France. Three years later, in 1902, the German chemist Friedrich Otto Giesel working independently of Debierne also discovered the element. Both scientists had been conducting experiments to find methods with which they could separate the rare earth elements from their oxides. The name actinium comes from the Greek word “aktinos” which means ray. Actinium is 150 times more radioactive than radium.

Actinium is found in extremely small amounts in uranium containing ores such as pitchblende. It is estimated that a ton of the mineral pitchblende would yield just 0.1 grams of actinium. This low natural availability means that if any quantity of the element is required it is cheaper and easier to produce it artificially. Actinium can be produced, within a nuclear reactor, by bombarding uranium with neutrons. Limited usage means that actinium is rarely produced and the global production is probably less than one gram.

Actinium is the lightest of the actinide or actinoid group of rare earth elements. It is one of only four elements in this group of fourteen that can be found occurring naturally. The other three naturally occurring actinides are the elements thorium, uranium and protactinium. All of the other actinides are man-made elements. The f-block of elements within the periodic table is made up of the actinides as well as the lanthanide or lanthanoid group of elements. All of the actinides and lanthanides are rare earth elements.

All of the isotopes of actinium are unstable. The most stable isotope, actinium-227, has a half-life of 22.7 years. Actinium-227 can decay in two ways. By beta decay actinium-227 will form thorium-227. Francium-223 can be formed by alpha decay of actinium-227. A total of thirty five isotopes of actinium have been recognized to date. The isotope with the shortest half-life so far discovered is actinium-216 with a half-life of 0.33 milliseconds.

Outside of the nuclear industry and research actinium has no economic uses. It is used to generate neutrons. Its high degree of radioactivity makes actinium a very real hazard to health so extreme caution must be taken when handling the element.