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This is protactinium.

Symbol Pa
Atomic number 91
Atomic mass 231.0359 amu

Protactinium was given the name protoactinium and was shortened to the present one in 1949. In 1913, while tracing the transmutation radioactive elements along the uranium decay series, scientists noted a brief transition between thorium-234 and uranium-234. The element was first called brevium or "brief". Other scientists at that time also located the same element and gave it more dramatic names such as uranium-X2. In 1917, several researchers independently found a longer-lived isotope of the element. From this sample, they wre able to determine more of the physical and chemical properties that are necessary for confirming the existence of a new element.

Distinguishing properties

Protactinium is a heavy, silvery-white and shiny metal. It oxidizes slowly in air. The small sample shown in the image is protactinium oxide.


Protactinium is found mixed with uranium ores such as pitchblende. The proportions are on the order of one part in ten million. The atomic energy commission of Great Britain had to process 60 tons of ore to get 125 grams of the metal. The cost at the time was on the order of $500,000.


Because the metal, as well as all of its compounds, is radioactive and poisonous, the element has no commercial application.

See also

Periodic table of the elements