Actinium

Actinium is chemical element 89 on the periodic table. Its symbol is Ac. Actinium's mass is 227 g/mol. 

Actinium is a silver radioactive, solid metal in actinide group. It is so radioactive that it glows in the dark. Even a small amount of actinium is dangerous to people.

History
Actinium was discovered in 1899 by André-Louis Debierne, a French chemist.  In 1899, Debierne described the substance as similar to titanium and (in 1900) as similar to thorium.

 Properties 
Actinium is a soft, silvery-white, radioactive metal. Its estimated shear modulus is similar to that of lead. Because its strong radioactivity, actinium glows in the dark with a pale blue light.

Actinium reacts quickly with oxygen and moisture in air forming a white coating of actinium oxide that stops the actinium from oxidizing.

 Isotopes 
Actinium that is found in nature is made up of two radionuclides 227Ac and 228Ac. Thirty-six radionuclides of actinium have been found. The most stable is 227Ac which has a half-life of 21.772 years. The shortest-lived known isotope of actinium is 217Ac which has a half-life of 69 nanoseconds.

 Occurence 
Actinium is only found in trace amounts in uranium ores. For example, one tonne of uranium ore contains about 0.2 milligrams of 227Ac. Thorium ores contain about 5 nanograms of 228Ac per one tonne of thorium.

 Uses 
225Ac is now being studied for use in cancer treatments. 227Ac is studied for use as an active element of radioisotope thermoelectric generators. 225Ac is used in medicine to make 213Bi in a reusable generator. It can be used in radiation therapy.

References

Category:Actinides